Gemstones of Tanzania by Gilay Shamika

2013 Sharing With Community

Gemstones of Tanzania Identification Brochure

Color, Transparency, Refractive Index, Specific Gravity, Spectrum, Inclusions and Rough Shape

Eng. Gilay Shamika


PREFACE

emstones have little attention in Tanzania compared to precious metals.

Precious metals especially gold, copper and silver are known to most of

Tanzanians and the business of the same is booming on daily basis. For

gemstones is different story. Few Tanzanians who know about gemstones. When you

talk about gemstones, few people will refer to Tanzanite, Ruby and garnets only. But

there are more types of gems in Tanzania.

This compilation is aimed to provide knowledge of gemstones which are cheaply

available in abundant compared to precious metals. On top of that, they also

command higher price than gold. The knowledge also will help Tanzanians to venture

into gemstones and hence diversification of minerals business. Rather than everybody

thinking of precious metals, Tanzanians can now start thinking of gemstones.

Tanzania is believed to be the second country with higher amount of gemstones

reserves after Madagascar. Gemstones are available in alluvial form along the river

banks, swamps, and natural dams and in the valleys where the gemstones are washed

out from the mountains by rainfall drains. Umber valley in Tanga is among the famous

valleys with alluvial gemstones. The compilation has shown the areas with gemstone

reserves. This will help if somebody has found the gems at a certain area, he/she can

refer to this compilation and see what kind of gemstones are found in that .Whenever

you see any colored stone within your vicinity, think about gemstones and not just

gravels or pebbles. Consult this compilation or any Minerals office for identification.

You might be playing with a gem worth a millions of dollars!

Talk to your children and ask them to fetch any colored stone along the river banks,

swamps and dams during their normal bathing games. The adults during grazing and

farming they may see such kind of stones. It is not a joke; the records show even

Dr.Williamsons found diamonds from indigenous who were blind about diamond. The

first diamond also at south Africa Kimberly, was found within the hand of child

playing with it as a normal pebble stone and one geologist saw it and the story

changes.Songea sapphire and Tunduru Alexandrite were discovered by missionaries.

The people thought those stones are evil because they don’t look like normal stones.

Rubies having red color, were thought to be bloody stone causing death and

alexandrite which changes color from Blue/Green to red, were thought to have

mysterious power. Therefore after arrival of Christianity, the Christians took those

stones to the priests (missionaries) to play for them and curse the devil not to bring

again those wicked stones. The priests were baffled and tell the Christians to keep

bringing those evil stones……..!! Knowledge is power, be the first to get knowledge in

every field, you never know when it will ripe.

G


Philosophy of Gem Business and Diamond Poem

For Gem Business Illiterates;

Gem Business is like Politics,

And,

Politics is like Gem Business.

Most of the People buy Gems by just trusting the seller about the benefits and features

of the merchandise (blind purchase concept). The Gem might be real or fake but they

just trust the seller’s words and close a deal. Politics is the same; you just trust the

politician’s words and vote for him/her. Both politics and Gem Business share the

same trait…..’Trust.’

But for Gem Business Literates;

Gem Business is a Science

And,

Science means Reality

Gems knowledge is a science which can be proved and confirmed, hence distinguished

from politics. The one with knowledge of gemstones is equipped with different skills to

identify and confirm what kind of jewelry/gem is. For him/her is not about trust but

reality. The only way to get this science is either to join a college or through private

studies, and get rid of being one of those who buy or deal with jewelry/gemstones

blindly. Devote your time and go through the whole compilation and for sure you will

definitely become ‘Gem Literate’.

Diamond Poem

Diamond is Durable than any gem,

Diamond is the most Desirable gem among others. And above all

Diamond is a real Deal. And for sure;

Diamond will never in any case let you into Desperation.

© Eng. Gilay Charles Shamika


IMPORTANT TERMS IN GEMSTONES

COLOR

In science color is a result of light wavelength when an object’s surface responds to

light. The object’s surface can absorb, transmit or reflect light. These responses are

the ones which results to the color we see. Human being can only see wavelength

between 750 and 380nm.In gemstones, color is the combination of hue, tone and

saturation.

Colored stones as the name itself signifies, color is the supreme criteria in judging and

grading colored stone. The hue, saturation and tone in their totality pave a way to a

premium.GIA has done a great job in expressing the real differences of those three

terms and how to identify them.

Hue: Hue is the color that we notice immediately like red, blue, yellow, or green.

Saturation is the intensity of the hue present in a color sensation. Colors of low

saturation are sometimes called weak, grayish or brownish while those of high

saturation are said to be highly saturated, strong or vivid. Saturation and Tone are

used to distinguish the ‘range of colors’ (range of hue) –is it deep blue, pure Blue or

slightly Blue.

Tone indicates the lightness or darkness of a color sensation. The scale ranges from 0

for pure black to 10 for pure white. Black and white and the grays between them are

called neutral colors. They have no hue. Colors that have a hue are called chromatic

colors. Colors that do not have a hue are known as achromatic.

In ancient histories color is related with happiness, grief, sorrow or misfortunes. In

Bible and Qur’an color also signifies something according to scriptures. In different

ceremonies colour is the one which determine the event at glance. Once you see black

colour and large crowd of people, you start thinking of something wrong. The flags of

nations have different colours not by accident but they hold the means and ways of

the struggle movements towards the independence.


For colored stones; color is the one which mostly bear the value of a particular

gemstone followed by other factors- 4Cs.


TRANSPARENCY

In common English a word transparency means Clearness, Simplicity, Openly,

Explicitly, Precision and Intelligibility. For English natives it might mean different but

the logic remains the same. The word ‘Transparency’ has gained momentum in

contemporary politics both in international and national forums. It is either related to

democracy or administration, for instance transparency in democracy practices or

transparency in administrative decisions.

Scientifically transparency means ability of material to transmit light. The gemstones

which allow light to pass through and enable observer to see through (clear), the

gemstones are said to be transparent. If totally the gemstone doesn’t allow light to

pass through is said to be opaque.

But there are other gemstones which are in between;

Transparency – Ability to transmit light

Semi-transparent – Capable of transmitting light with some distortion, so an object

viewed through the material is indistinct.

Translucent – Capable of transmitting and diffusing light so an object viewed through

the material cannot be distinguished.

Semi-translucent – Capable of transmitting light only through thin area usually at

the edge.

Opaque – Inability of transmitting light.

HEFT OF GEMSTONES:

Heft means how heavy a gemstone is when you feel it in your hand. The

heaviness of a gemstone differs according to their crystal formation.


INCLUSIONS AND PHYNOMENA

The meaning of Inclusion

The inclusions are virtually materials other than original gemstones. They may be

formed before, after or on the same time with the gemstones. Broadly is defined as;

Any irregularity or dislocations in a crystal's lattice, or structure, marks of the

crystallization phases, color striations, and internal fractures, which may be caused

by internal stress or external pressure; Simply the material trapped within the body of

a crystal which is different from the primary elements of the host crystal.

Types of inclusions commonly found in gemstones

Crystal’s feathers, needle like, cracks, healed fractures and included lily pads and foils.

Individual pinpoints, included crystals, voids Clusters of included crystals, or voids Clouds of pinpoints

There are three types of inclusions, or processes, through which other materials can get into a crystal;

Protogenetic Inclusions: These inclusions were already present before the host mineral was formed. The host mineral grew around them. Therefore they are older than the host crystal.

Syngenetic Inclusions: Formed at the same time as the host mineral. These inclusions can be solids, liquids, or gases, or combinations of any of the three forms of matter. These inclusions are therefore the same age as the host crystal.

Epigenetic Inclusions: These inclusions were formed after the host crystal was formed. These inclusions are usually either formed by exsolution or from the recrystallization of a fracture in a host mineral. They may also be liquid, solid, or gaseous. These inclusions are therefore younger than the host crystal.


PHENOMENA

Phenomena are unusual display of gemstones in response to light. It is optical effects

caused by reflection, interference or refraction. The phenomena effects increase the

price of the gemstones; customers like buying something two-in-one, normal gemstone

and phenomenal gemstone when light is directed on a gemstone.

Types of Phenomena Effects

Asterism: Appearance of a star on the surface of a gem when light reflecting from

minute needle-like inclusions in a gem.

Adularescence: Appearance of blue-white light in moonstone caused by thin fibrous

or layers in moonstone by diffracting, diffusing and interfering the light.

Aventurescence: Appearance of glittering spots of color caused by light reflections

due to platelets inclusions.


Chatoyancy: Appearance of cat’s eye resemblance on gemstone surface after light

being reflected by minute parallel needle-like inclusions, fibrous or parallel tubes

inclusions depending on the gemstones. In other word; Phenomenon of certain Cat's

eye minerals which causes them to exhibit a concentrated narrow band of reflected

light across the center of the mineral. Chatoyancy is almost exclusively exhibited on

polished cabochons.

Color change: Change of color of a gemstone body when different sources of light are

applied (incandescent and fluorescent).

Play-of-color: Appearance of flashes of spectral colors (rainbow colors) in opal when

minute silica spheres in opal cause diffraction interference of light.

Iridescence: Appearance of interference colors seen in agates and other gemstones.

But mostly, the term is for agates.

http://www.minerals.net/Mineral_Glossary/Cat's_eye.aspx

http://www.minerals.net/Mineral_Glossary/Cat's_eye.aspx

http://www.minerals.net/Mineral_Glossary/polished.aspx

http://www.minerals.net/Mineral_Glossary/cabochon.aspx


Orient: Orient logically is iridescence phenomenon but when occur in pearls, is called

orient. Therefore orient is iridescence in pearl.

Labradorescence: Appearance of broad color flash across the surface of Labradorite

feldspar. This occurs when the thin layers in Labradorite cause light interference.


REFRACTIVE INDEX (RI)

Refractive Index (RI) is the ration of speed of light in the air (vacuum) to the speed of

light in a medium.

SINGLE REFLECTION (SR): Is the optic property of a gemstone to exhibits a single

reading on the refractometer. The reading does not change even if you turn the

gemstone on the refractometer. If you use the polarizing filter, when you turn the gem

under the polarizing filter, the gem’s light reflection intensity remain the same.

DOUBLE REFLECTION (DR): Is the optic property of a gemstone to exhibits a

double/more than one reading on the refractometer - the maximum and minimum

readings on the refractometer. The readings change as you turn or move the

gemstone on the refractometer. If you use the polarizing filter, when you turn the gem

under the polarizing filter, the gem’s light reflection intensity change.

GEM REFRACTIVE INDEX (RI) IS LIKE HUMAN FINGER PRINT

The RI is the most useful method in identifying gemstones. Garnet and Ruby can be

quickly distinguished by SR or DR. All Garnets are single reflective (SR) while Rubies

are double reflective (DR).

Gemstone’s RI is like finger print for human being. There is no way, a finger print of

one human being to resemble with others. The same for gemstones; each gemstone

has its own RI. It is only possible for RI of one gemstone to overlap with other

gemstones and having the same birefringence but rarely to be the same.


GEMSTONES SURFACE APPEARANCE

Gemstones surface exhibit different appearance when cut and polished. The

differences are contributed by texture and structure of the gemstones crystal lattice-

hardness.

Luster is the term used to describe how does the surface of faceted gemstone look like

in reflected light.

High luster: The gem surface shines like mirror. This includes diamond, hematite,

and Zircon and demantoid garnet.

Hematite luster is called Metallic: Mirror like luster

Diamond Luster is called Adamantine: the highest luster for all transparent gems

Demantoid garnet and Zircon Luster is called Sub adamantine: Not sharp like

adamantine.

Medium luster: The gem surface shines like glass or slightly like glass (Vitrous and

Sub-vitrous).Most transparent gemstones belong to this luster.

Low luster: The gem surface looks like Greasy, Resinous, Waxy and Dull.

Sheen Luster: The shines of the gem occur just below the gems surface. The reflection

is seen as if is inside the gem surface and look Silky/ Pearly.

SYNTHETICS AND SIMULANTS

Simulant means naturally look like. These are gems which occur naturally and used

to imitate other gemstones. For example colorless natural sapphire, quartz, topaz and

rocky crystal are sometime used as diamond simulant, while;

Synthetics are manmade gemstones with the same chemical and physical properties

as natural gemstones they imitate. They are made in Laboratory.


GEOMETRY OF ROUGH GEMSTONES

1. Meaning of Geometry in mathematics

In mathematics geometry topic is among the difficulty. Is about how angles are related

to shapes, area and lengths of an object. I remember in my Ordinary and high school

it takes ages of time to understand this topic; especially the logic behind Angle of sine,

cosine, tangents etc.

The scientists also have taken centuries to find the simplicity of geometry calculation.

The most complicated geometry involves curved, domed and circular objects. The early

mathematicians struggled a lot and some discovered pie (π), Angle of sine, cosine,

tangents and other constants to simplify geometry of those complicated objects. The

discovery of Calculus to some extent makes life easy but for others is even worse……..!

Archimedes takes not less than 20 years to find geometry of curved objects but he was

killed before he completed his work. When roman police came to arrest him he said

‘please do anything to me but don’t disturb my circles’. His room was full of

drawings of curved objects trying to find the easy way of calculating angles, areas and

lengths. Curved and hanging bridges, domed and curved buildings, enjoy this topic in

engineering and architectural calculation before erected.

2. Meaning of Geometry in Gemstones

In gemstones, geometry means the same as in mathematics. It means a shape of

rough gemstones (crystal shape). Each rough gemstone has its habit naturally

(crystal shape). The occurrence of Moonstone shape is expected to be different from

corundum and other gemstones.

There are occurrences of seven crystal systems (shapes) in gemstone as summarized

in the next pages;


Source: http://www.realgems.org

1. Cubic or Isometric – It is assumed all sides and length to be the same but not

always. Sometime octahedrons (eight faces) and dodecahedrons (10 faces) are

found into this crystal shape.

2. Tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms.

3. Orthorhombic - like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms or dipyramids (two pyramids stuck together).


4. Hexagonal - six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon.

5. Trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division.

6. Triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.

7. Monoclinic - like skewed tetragonal crystals, often forming prisms and double

pyramids. This is a very simplified view of crystal structures

Some example of roughs with typical crystal system

http://chemistry.about.com/od/crystallography/ig/Bravais-Crystal-Lattices/Rhombohedral-Crystal-Lattice.htm

http://chemistry.about.com/od/crystallography/ig/Bravais-Crystal-Lattices/Triclinic-Crystal-Lattice.htm


RUBY BACKGROUND

uby Name History: The name ruby comes from Latin word ruber, which

means red. In Sanskrit which is Indian language, ruby is termed as ratnaraj

which means King of Gems.

Colour Ranges: Ruby comes from Corundum group. According to GIA, for the

corundum to be called ruby, it should be deep, pure vivid red. This depends on the

combination of hue, tone and saturation. But in other geographical area even pinkish,

purplish or orange red sapphire are called rubies. Therefore the distinction depends

on the geographical areas. But professionally deep, pure, vivid red is ruby.

Varieties: Ruby and Sapphire are varieties of Corundum group. The difference is

colour. Ruby is red while sapphire is Blue. Sapphire has other fancy colours, like

Songea Orange colour, etc.

GEM IDENTITIES AND GEOMETRY OF ROUGH

Refractive Index (RI): DR 1.762 to 1.770 Specific gravity (SG): 4.00 Hardness: 9 Moh’s scale Inclusions: needle like rutile inclusion, fingerprint inclusions, high or low relief inclusions, two phase inclusion, straight and hexagonal growth banding, angular color banding and twining lines.

R


TREATMENT

Heating: To improve color or clarity appearance

Lattice diffusion: This is a process of heating ruby to very high temperature in the

presence of a coloring agent. The aim is either to increase colour appearance, remove

color or change to other colour.

Fracture filling: Is a process of filling fractures of ruby by using oil or proxy resin.

The purpose is to improve clarity and also hide fractures.

Cavity filling: Is the same as fracture filling but cavity is large and filling it may result

in weight addition.

SYNTHETICS/SIMULANTS/IMITATION

Imitation: Glass

Confuse with: Spinel, Tourmaline, Garnets, Topaz

RUBY DEPOSITS IN TANZANIA

Morogoro: Mwalazi, Ngongolo, Matabe, Mayote,

Mvomero,Matombo,ulanga(chipa,mahenge,Lukande,Epauko)

Dodoma: Winza, Malamo, Madengi,matumbulu,mlali,mleha,Kongwa(pandambili) and Mangalisa

Tanga: Kalalani, Kofi Mountains and Umber River valley

Manyara: Hanang (dudumera), Monduli ,Mundarara

Kilimanjaro: Same (Lolobukoand North pare Mts)

Pwani: Bagamoyo(mandera)

Ruvuma: Mbinga (Likombe)


SAPPHIRE BACKGROUND

apphire Name History: Sapphire name originates from Greek work Sappheiros.

Before Greeks mixed lapis lazuli and blue sapphire with one name ‘Sappheiros’

because both have the same color.

Color Ranges: Sapphire has many colours but when the word Sapphire is used alone

it means sapphire with blue colour. Sapphire with other colour than blue (fancy

sapphire) need to have pre-fix of color for instance, Orange sapphire, Pink sapphire,

Purple sapphire.

Varieties: Sapphire is a variety of Corundum with the same geological properties like

ruby the difference being only colour. Ruby red while sapphire Blue and other colours

– fancy sapphires (orange, pink, purple, colorless, grayish etc). The Orange sapphire

from Songea Tanzania is among the expensive fancy sapphire after pink.


Refractive Index (RI): 1.762 to 1.770 Specific gravity (SG): 4.00 Hardness: 9 Moh’s scale Inclusions: needle like rutile inclusion, fingerprint inclusions, high or low relief inclusions, two phase inclusion, straight and hexagonal growth banding, angular color banding and twining lines.

TREATMENT

Heating: To improve color or clarity appearance

Lattice diffusion: This is a process of heating sapphire to very high temperature in

the presence of a coloring agent. The aim is either to increase colour appearance,

remove color or change to other colour. It creates any colour in Corundum.

S


Irradiation: This bombardment of electrons which cause energy release. The process

is used to change colorless corundum to yellow or orange. But the color is not

permanent. It fades with time.

Fracture filling: Is a process of filling fractures of ruby by using oil or proxy resin.

The purpose is to improve clarity and also hide fractures.

Cavity filling: Is the same as fracture filling but cavity is large and filling it may result

in weight addition.

SYNTHETICS/SIMULANTS/IMITATION

Imitation: Glass

Synthetics: Flame fusion sapphire, Flux sapphire, Hydrothermal sapphire, Floating zone

sapphire.

Confuse with: Amethyst, Kunzite, Tanzanite, Spinel, Zircon, Topaz, Tourmaline, dAquamarine.Chrysoberyl, etc

Fancy Sapphire Confuse with: Citrine, Alexandrite, Rhodolite garnet, Spessartite garnet, Malaya garnet.

SAPPHIRE DEPOSITS IN TANZANIA

Lindi: Nachingwea Lumesule, Tunduru

Morogoro: Mahenge

Tanga: Umba valley

Dodoma: Winza


EMERALD BACKGROUND

merald Name History: The name comes from Greek word meaning green

Color Ranges: Emerald has only green color; it is a beryl with green color.

Variety: Emerald belongs to beryl group which has two varieties – Emerald and

Aquamarine. Aquamarine is a blue beryl while Emerald is a green beryl.


Refractive Index (RI): DR 1.577 to 1.583 Specific gravity (SG): 2.72 Inclusions: the gem with the most cracks and inclusions; three and two-phase inclusions, fingerprint inclusions, liquid filled inclusions, tube and needle like inclusions, calcite inclusions, angular growth zoning, minerals/crystals inclusions. Hardness: 7.5 to 8

TREATMENT

Fracture filling: filling surface-reaching fractures with colorless oils or resins. Almost

95% of Emeralds are fracture filled because the occurrence of emerald is associated

with fractures and inclusions.

SYNTHETICS/SIMULANTS/IMITATION/ALTERNATIVES

Imitation: Green glass, Synthetic spinel triplet

Synthetic: Flux emeralds, hydrothermal emeralds

Alternatives: Demantoid garnet, Tourmaline, Diopside, Jadeite, Peridot, Zircon,

Tsavorite garnet, Alexandrite

EMERALD DEPOSITS IN TANZANIA:

Manyara: Mbulu Kagera: Karagwe –kyerwa

Morogoro: Mt. Nguru Rukwa: Sumbawanga-Mponda

E


AQUAMARINE BACKGROUND

quamarine Name History: Latin name –water of the see due to its color being

the same as seawater – light blue.

Color Ranges: ranges from light blue to dark blue and blue-green


Refractive Index (RI): DR 1.577 to 1.583 Specific gravity (SG): 2.72 Inclusions: hollow or liquid filled tubes, fingerprints and two/three phase inclusions. It occurs also as eye-clean Hardness: 7.5 to 8

TREATMENT

Heat treatment change light color aquamarine to get the desired dark blue

aquamarine.

Confuse with: Topaz, Kyanite, Tourmaline and Zircon

AQUAMARINE DEPOSITS IN TANZANIA:

Ruvuma: Tunduru

Manyara: Mbulu

A


ZIRCON BACKGROUND

ircon Name History: Persian language – golden colored

Color Ranges: It has wide range of color- colorless, strong blue, green-blue, yellow,

brown, orange, red, violet. The most occurrences are strong blue and green-blue with

green color component.


There are two types of Zircon - Higher and Lower Zircon. Blue zircon is said to be with high properties – strong doubling and high RI. Green zircon is said to be with low properties – no doubling and may show SR with SG 4.5 to 4.70 or 3.95 to 4.20. Refractive Index (RI): DR OTL Specific gravity (SG): 3.90 to 4.73 Inclusions: any natural inclusions possible Hardness: 6.5 to 7.5 Spectrum: Zircon with blue hue usually shows a key line at 653.5nm (known as

zircon line) with other lines up to 40’s.

Confuse with: Aquamarine, Topaz, Chrysoberyl, Tourmaline, Idocrase, Demantoid,

Hessonite, Diamond and Sapphire

ZIRCON DEPOSITS IN TANZANIA

Singida Kiomboi Iramba and Eshamwala

Morogoro: Ulanga

Tanga: Mashewa and Mavumbi

Dodoma: Winza Mpwapwa

Rukwa: Namanyere and Paramawe

Z


KYANITE BACKGROUND

yanite Name History: Kyanite means blue.

Color Range: Kyanite has most occurrence color is Strong blue, sometime with tints of

purple. It rarely also occur as colorless, blue-green to brown.


Refractive Index (RI): DR 1.716 to 1.731 Specific gravity (SG): 3.5 to 3.7 Inclusions: Any natural inclusions possible Hardness: 4.5 to 5.0 Moh’s scale

Confuse with: Sapphire, Tanzanite and Amethyst

KYANITE DEPOSITS IN TANZANIA

Arusha: Monduli.Manyara: Kwaraha and Sidi Hill

Morogoro: Idibo Kilosa

Tanga: Makalingi, Kitwai, Hakichoo, Gologolo

Kilimanjaro: Hedaru, Chabaruti, Chankunku

Rukwa: Namanyere, Tambaluka, Kisi, Chala.

K


TANZANITE BACKGROUND

anzanite Name History: Since Tanzanite is only found in one source in the

world, Tanzania East Africa. Tiffany & Co the main distributor decided to name

it by referring to the country of origin.

Colour Ranges: Tanzanite crystal occurs as a transparent rough with different colours

including brown, blue, greenish-blue and khaki. But the most common is the one with

blue colour. Predominantly blue tanzanite is generally worth more than other hues.

The deep blue (A- grade) is obtained by heating tanzanite in controlled temperature

but also they occur naturally.

Tanzanite has distinguished property of showing three colors at different angles

(Trichrinic)

Varieties: tanzanite comes from Zoisite group. Before discovery of Tanzanite the only

Zoisite varieties known were Thulite and Anyolite.


Refractive Index (RI): DR 1.69 to 1.70 Specific gravity (SG): 3.35 Inclusions: Often inclusion free but can include fine needles, pinpoints and clouds. Hardness: 6.5 to 7

TREATMENT

Heating: Produce colors that include light to dark Violetish blue and bluish purple, as

well as pure blue. But these colors also occur naturally.

Confuse with: Sapphire, Kyanite, Amethyst

TANZANITE DEPOSITS IN TANZANIA:

Manyara: Merelani Tanzania

T


TOURMALINE BACKGROUND

ourmaline Name History: Tourmaline name comes from toramalli which

means mixed gems in Sinhalese language of Sri Lanka.

Color Ranges: Tourmaline comes in a wide range of colors. It is believed to be a gem

with widest color ranges of any gem species.

Varieties: Tourmaline exists in six varieties categorized by their colours.

1. Rubellite tourmaline 2.Indicolite tourmaline

3. Chrome tourmaline 4.Parti-colored tourmalines

T


5. Watermelon tourmaline 6. Paraiba tourmaline


Refractive Index (RI): DR 1.624 to 1.644 Specific gravity (SG): 3.06 Inclusions: color zoning, thread like inclusions, gas filled fractures. Hardness: 7 to 7.5 Moh’s scale

SYNTHETICS/SIMULANTS/IMITATION:

Glass, Synthetic Ruby, Synthetic Sapphire, Synthetic Spinel

Confuse with: Any gemstones because tourmaline has all colors.

TOURMALINE DEPOSITS IN TANZANIA:

Kagera: Karagwe –kyerwa

Dodoma: Mpwapwa-Winza, Chamwino (Hombolo)

Mtwara: Newala

Tanga: Handeni-Makwere, Muheza (Ng’ombeni)

Manyara: Kiteto


ALEXANDRITE BACKGROUND

lexandrite Name History: Alexandrite was first discovered in Russia in the

early 1800's. It was named in honor of Alexander Nicholavich, who was later to

become the Russian Czar Alexander II. Legend has it that the gemstone was

discovered on the future Czar's birthday and named in his honor, though the

factual nature of this is disputed.

Color Ranges: Blue in daylight and red/purple in incandescent light. Alexandrite is

the highly regarded color changing variety of Chrysoberyl. The color of Alexandrite

changes under different lighting conditions. If viewed in daylight, its color is greenish

blue to dark yellow-green. If viewed in incandescent or candle light, its color is pink to

red. Alexandrite is a very rare and highly valuable gemstone, and until recently was

extremely difficult to obtain due to its rarity. However, new sources in Brazil and

Tanzania have made this gemstone available and more mainstream on the gemstone

market.


Refractive Index (RI): DR 1.744 to 1.755 Specific gravity (SG): 3.5 to 3.80 Inclusion: Not diagnostic – any inclusion possible. Hardness: 8.5

Confuse with: Color change Sapphire and color change Garnet

ALEXANDRITE DEPOSITS IN TANZANIA

Ruvuma: Tunduru

A


CHRYSOBERYL BACKGROUND

hrysoberyl Name History: Chrysoberyl is a hard, tough, and durable gem.

Although lacking the fire of other gemstones, Chrysoberyl in its various

forms can be quite valuable.

Color Ranges: Most Chrysoberyl gems are yellow, though some are brown, green, or

orange.

Varieties: Chrysoberyl is best known for its important varieties Alexandrite and Cat's

Eye. Alexandrite is a rare and expensive form that exhibits different colors in natural

and artificial light. Cat's Eye is Chrysoberyl that is polished into a cabochon and

highly chatoyant, displaying a sharp line of light through the center of the stone.


Refractive Index (RI): DR 1.744 to 1.755 Specific gravity (SG): 3.5 to 3.80 Inclusion: Not diagnostic – any inclusion possible. Hardness: 8.5

Confuse with: Topaz, Tourmaline, Zircon

CHRYSOBERYL DEPOSITS IN TANZANIA

Ruvuma: Tunduru

C


TURQUOISE BACKGROUND

urquoise Name History: The name refers to French expression Pierre

Tourques (Turkish Stone).

Color Ranges: The color ranges from light to medium blue or greenish blue. It is often

mottled and sometimes has dark splotches. But can also occur without being mottled

or splotches.

GEM IDENTITIES AND GEOMETRY OF ROUGH;

Refractive Index (RI): 1.610 to 1.650 Specific gravity (SG): 2.74 Inclusions: mottled with dark splotches recessed below the surface. Hardness: 5 to 6 Moh’s scale TREATMENT

Impregnation with wax, plastic or dye added: To improve color, luster and

durability.

Backing with Epoxy resin: Adds thickness, strength and weight.


Imitations: Glass, Plastic, Reconstructed turquoise

Confuse with: Agate, Chrysocolla in Chalcedony, Jadeite, Lapis lazuli, Malachite and

Nephrite.

DEPOSITS IN TANZANIA

Tanga: Muheza – Gerevi-Hills

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PERIDOT BACKGROUND

eridot Name History: The name originated from Arabic word Faridat, which

means gem. It is also called Olivine or Chryolite.

Colour Ranges: Occurs as brownish or yellowish green to greenish yellow


Refractive Index (RI): DR 1.654 to 1.690 Specific gravity (SG): 3.34 Inclusion of natural Peridot: Disc like liquid and gas inclusions commonly called lily

pads. High relief black chromites crystal inclusions.

Hardness: 6.5 to 7 Moh’s scale


Imitations: Glass, Plastic, Synthetic sapphire, Synthetic Spinel

Confuse with: Demantoid garnet, Emerald, Tsavorite garnet, Zircon, Topaz,

Tourmaline, Jadeite, and Chrysoberyl.

PERIDOT DEPOSITS IN TANZANIA

Manyara: Mbulu- Kingiti Dodoma: Kibakwe Arusha: Leishaine Hill.

P


APATITE BACKGROUND

patite Name History: Apatite in Greek means ‘to deceive’. Apatite confuses with

tourmaline and has RI close to tourmaline which can deceive you.

Colour Ranges: Occurs in variety of colour ranges. Colorless, Pink, Yellow, Green,

Blue and Violet. Apatite is a fairly uncommon gemstone, and you will only rarely see it

offered for sale in the typical commercial jewelry stores.


Refractive Index (RI): DR 1.634 to 1.638 Specific gravity (SG): 3.18 Inclusions of natural Apatite: crystals, needles, two and three phase inclusions.

Hardness: 5 Moh’s scale

Confuse with: Aquamarine, Topaz, Zircon, Demantoid Garnet, Tsavorite

APATITE DEPOSITS IN TANZANIA

Manyara: Hanang- Gallapo

Tanga: Korogwe-Umber Valley

Dodoma: Mpwapwa

Mbeya: Chamloto

Mtwara: Newala- Nagaga

A


SPHENE BACKGROUND

phene Name History: The name sphene comes from greek word meaning wedge

since its crystal shape looks like wedge.

Colour Ranges: Sphene occurs in variety of color range from yellow, brown, green and

reddish brown.


Refractive Index (RI): DR OTL Specific gravity (SG): 3.52 Inclusions: All natural inclusions are possible

Hardness: 5 to 5.5 Moh’s scale

Confuse with: Demantoid garnet, Citrine, Apatite, and Tourmaline

SPHENE DEPOSITS IN TANZANIA

Tanga, Dodoma and Morogoro.

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TOPAZ BACKGROUND

opaz Name History; The source of word topaz comes from Greek Topazios,the

old name of an Island in Red Sea which used to be a source of Peridot. Topaz

was confused with peridot before advancement of gemstones identifications

kills.

Colour Ranges: The color ranges from Colorless, Yellow, Brown, Reddish, Pink and

Orange

Varieties: Topaz has no variety but just trade names

Imperial Topaz: Medium reddish Orange. The most expensive topaz.

Sherry Topaz: Yellowish brown or brownish yellow to Orange.name comes from the

color of sherry wine. To get rid of confusion with citrine and smoky quartz, Topaz with

this color range is also called precious topaz.


Refractive Index (RI): 1.619 to 1.627 Specific gravity (SG): 3.53 Inclusions: Two and three phase inclusions, liquid inclusions in its planes Hardness: 8 Moh’s scale

TREATMENT

Heating: Changes some yellow, Orange, brown topaz to Pink

Irradiation followed by heat: Produces various shades of blue from colorless.

T



Imitations: Glass, Synthetic Sapphire, Synthetic Spinel

Confuse with: Aquamarine, Citrine, Tourmaline, Sapphire, Smoky Quartz, Hessonite

garnet, Morganite, Zircon, Kunzite, Spessartite garnet, Malaya garnet.

TOPAZ DEPOSITS IN TANZANIA

Dodoma: Winza Mpwapwa Tanga: Handeni Kwendikundi Plain


IOLITE BACKGROUND

olite Name History: Iolite means violet in Greek language. It is also sometime called

Cordierite

Blue Iolite Purple Iolite

Color Ranges: It ranges from light to dark blue, brown and violet. Since it is

pleochroic, it shows different color from different viewing angles. Depending on the

angle, iolite appears colorless, gray or yellow. Navigators are said to use iolite as light

polarizer to locate the sun.


Refractive Index (RI): DR 1.542 to 1.551 Specific gravity (SG): 2.61 Inclusions: Hematite inclusions, natural inclusions



Imitation: Glass

Confuse with: Blue Topaz, Amethyst, Sapphire, Tanzanite and Purple/Blue Scapolite

IOLITE DEPOSITS IN TANZANIA

Manyara: Babati, Hanang

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SPINEL BACKGROUND

pinel Name History: The name’s origin is unknown. This is due to spinel being

under estimated and under appreciated by many people during early civilization. The

confusion of spinel with Rubies draws back its popularity by being referred to ruby. It

is among the rare gemstones and hence less known in a market.

Color Ranges: The color ranges from violet, blue, orange, red, pink and purple. Spinel

in most cases appears red and found in the same sources with rubies. It can also

appear as color change from grayish blue in daylight to purple in incandescent light.

Varieties: No variety but it is believed that Spinel is the most synthesized gem used

to imitate other gemstones in the market.


Refractive Index (RI): SR 1.718 Specific gravity (SG): 3.60 Inclusions: minute octahedral or negative crystals, alone or in fingerprint pattern;

included crystals, iron oxide staining.



Imitation: Synthetic Sapphire, Glass, Synthetic Ruby

Synthetics: Flux and Flame fusion Spinel

Confuse with: Garnets, Ruby, Tourmaline, Topaz, Aquamarine, Amethyst, and

Kunzite.

SPINEL DEPOSITS IN TANZANIA

Morogoro: Mahenge, Ulanga Dodoma: Winza Ruvuma: Tunduru

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SCAPOLITE BACKGROUND

capolite Name History: The name Scapolite is derived from the Greek words

scapos, which means rod, and lithos, which means stone. The natural crystal often

looks stick-like, hence it's name. Scapolite is a little known gemstone that can be quite

beautiful. The most common colors are a nice yellow to orange to pink or violet.

Scapolite is a distinctly fibrous gemstone and is often confused with amethyst, citrine,

Chrysoberyl and golden beryl.

Color Ranges: occur in different colors including Colorless, yellow, pink, violet


Refractive Index (RI): DR 1.550 to 1.564 Specific gravity (SG): 2.60 to 2.68 Inclusions: Natural inclusions


Confuse with: Amethyst, Tanzanite, Iolite

SCAPORITE DEPOSITS IN TANZANIA

Dodoma: Imagi, Tambi

Tanga: Umba korogwe

S

http://www.ajsgem.com/information/Amethyst-64.html

http://www.ajsgem.com/information/Citrine-66.html

http://www.ajsgem.com/information/Chrysoberyls-89.html


GARNET BACKGROUNDS

During my study at Gemological Institute of America (GIA), garnet varieties

identification was one of my weakness points. I know at a glance that, it is a garnet

but which one……Pyrope, rhodolite, Almandite, Pyrope-Almandite, Hessonite etc!!

My instructor Annie did a tremendous job for me to master garnet varieties

identification. Eventually everything was on a right track and my classmates used to

tease me --- King of garnet. In my practical Exam of 20 stones, I picked up three

garnets and I was able to identify their varieties. Spectrum is the most useful tool for

garnet varieties identifications, especially for those combined garnets.

Green garnet Red garnet Mandarin garnet Mali garnet


DEMANTOID GARNET BACKGROUND

emantoid Name History: In Dutch language, demantoid means Diamond like. It is

called diamond- like because it shows flashes of rainbow color (fire) like diamond.

Demantoid flashes are more noticeable compared to diamond.

Color Ranges: Green to yellow-green


Refractive Index (RI): SR 1.88 (OTL) Specific gravity (SG): 3.84 to 3.91 Inclusions: Mostly with horsetail like inclusion (radiating needle-like inclusions, but

not in all demantoid)



Imitation: Garnet and glass doublet, Colored CZ, Colored YAG

Confuse with: Emeralds, Peridot, Tsavorite garnet, Tourmaline, Green Zircon, and

Green Sapphire.

DEMANTOID DEPOSITS IN TANZANIA

No discovery at present

D


TSAVORITE GARNET BACKGROUND

savorite Name History: The name refers to Kenya Tsavo National Park where the gem

is abundantly found. Merelani area apart from being the only source of Tanzanite, it

also host some Tsavorites.TanzaniteOneMining Ltd (TOML as it is called by TMAA)

encounters the Tsavorite when mining Tanzanite.

Color Ranges: The color ranges from light to intense green to yellowish green. It is

used mostly as alternative to Emeralds .Since the stone is not treated it is favored by

many customers who like green color.


Refractive Index (RI): SR 1.740 (Can be low up to 1.735 Specific gravity (SG): 3.61 Inclusions: Fingerprints, graphite platelets, liquid and minerals inclusions and healed fractures Hardness: 6.5 to 7 Moh’s scale


Imitation: Synthetic Spinel, Synthetic Emerald and Glass

Confuse with: Peridot, Tourmaline, Demantoid garnet and Emerald.

TSAVORITE DEPOSITS IN TANZANIA

Manyara: Merelani, Simanjiro -Lemshuku

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GROSSULARITE (GROSSULAR/GREEN) GARNET BACKGROUND

rossularite Name History: The name grossularite in Latin is gooseberry.

Color range: Near-colorless, Yellowish Green or green. Tsavorite and green garnet

(grossular) are all variety of grossularite. The difference is their color intensity.

Tsavorite is medium light to dark green, while grossularite is light yellowish green.


Refractive Index (RI): 1.735 to 1.759 Specific gravity (SG): 3.61 Inclusion: Fingerprints, graphite platelets, liquid and minerals inclusions and healed fractures Hardness: 7 Moh’s scale

NB: Grossularite- andradite garnet (mali garnet) is Yellowish green also with RI

1.773 to 1.779 while with RI 1.773 to 1.779 and yellow only , is also Grossularite

garnet


Imitation: Glass

Confuse with: Tsavorite, Tourmaline, Demantoid garnet and Emerald.

GREEN GARNET DEPOSITS IN TANZANIA

Manyara: Simanjiro –Lemshuku

Dodoma: Mpwapwa

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HESSONITE GARNET BACKGROUND

essonite Name History: The information about hessonite name is quite unknown.

Whatever the meaning of the name it is, hessonite is a variety of grossularite garnet

like tsavorite. It is also known as Cinamon Stone in market.

Color Ranges: medium to dark orange to yellow, yellow-green, brownish orange and

colorless.

NB: If pale call it grossularite not hessonite


Refractive Index (RI): SR 1.740 (can go up to 1.755) Specific gravity (SG): 3.61 Inclusions: heat wave effect (looks like undulating growth, burnt area or some call it scotch in water effect) and rounded crystals.



Confuse with: Citrine, Spessartite, Almandite, Zircon, Topaz, Orange Sapphire and

Fire Opal.

HESSONITE DEPOSITS IN TANZANIA

Morogoro: Kilosa, Uluguru mount, Mngazi valley, kisitwi

Tanga: Mlola Lushoto, Kilinga and Kihunza Handeni

Ruvuma: Likombe Mbinga

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SPESSARTITE GARNET BACKGROUND

pessartite Name History: The name comes from Spessart which is a district in

Bavaria State, German that was the first source of a gem.

Color Ranges: It is among garnet gem which is not red as most people know all

garnets are red – but it is not. (Always with orange component). Spessartite color

ranges from medium – light to dark Orange, yellowish, brownish or reddish Orange.


Refractive Index (RI): SR 1.810 (OTL) Specific gravity (SG): 4.15 Inclusions: heat wave effect (looks like undulating growth, burnt area or some call it

scotch in water effect) and rounded crystals

Hardness: 7.25 to 7.5 Moh’s scale


Imitation: Synthetic Sapphire, Glass

Confuse with: Citrine, Fire Opal, Spinel, Topaz, Tourmaline, Malaya Garnet,

Carnelian, Amber.

SPESSARTITE DEPOSITS IN TANZANIA


Morogoro: Kisitwi Kilosa, Kihunza, Mngazi valley, Uluguru Mts,

Tanga: Mlola Lushoto, Kilinga Handeni.

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RHODOLITE GARNET BACKGROUND

hodolite Name History: The name derived from Greek words, rhodo, rose and lithos,

meaning stone. Geologically, rhodolite is a mixture of Almandite and Pyrope garnets.

Color Ranges: predominantly purple but also occur in a range of light to dark

purplish red through reddish purple.


Refractive Index (RI): SR 1.750 to 1.780 Specific gravity (SG): 3.84 to 3.88 Inclusions: Low relief crystals, needle inclusions, zircon crystals with strain halos.



Imitation: Synthetic ruby and Glass

Confuse with: Topaz, Almandite, Pyrope, Spinel, Zircon, Tourmaline, Ruby.

RHODOLITE DEPOSITS IN TANZANIA

Manyara: Lelatema kiteto

Morogoro: Uluguru mts, Mngazi

Ruvuma: Likombe

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PYROPE GARNET BACKGROUND

yrope Name History: In Greek language, pyropos means fiery eyed. The gem was

called pyropos (fiery-eyed) because of having glowing red color. Sometime in market is

called Bohemian garnet.

Color Ranges: The color ranges from medium to dark reddish orange to purplish red.


Refractive Index (RI): SR 1.730 up to 1.750 Specific gravity (SG): 3.78 Inclusion: needle-like, crystals and irregular rounded crystals.



Imitation: Synthetic ruby and Glass

Confuse with: Topaz, Almandite, Rhodolite, Pyrope, Spinel, Zircon, Tourmaline, and

Ruby.

PYROPE DEPOSITS IN TANZANIA

Tanga: Mlola Lushoto and Kilinga Handeni

Dodoma: Tambi Mpwapwa

Morogoro: Kisitwi, Kihunza, Mngazi and Uluguru mts.


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ALMANDITE GARNET BACKGROUND

Almandite Name History: The Almandite was named after the town of Alabanda in

Asia which was a center for trading and faceting gemstones from different places.

Color Ranges: The color range from orange red through red to reddish purple. It is

mostly fashioned as hollowed cabochons to increase color intensity- more reddish.


Refractive Index (RI): SR 1.781 to OTL Specific gravity (SG): 4.05 Inclusion: zircon crystals having strain halos, high or low relief crystals and Needle-

like inclusions.



Imitation: Garnet- and- glass doublet

Confuse with: Hessonite, Spessartite, Rhodolite, Pyrope, Spinel, Tourmaline, Ruby.

ALMANDITE GARNET DEPOSITS IN TANZANIA

Tanga: Mlola Lushoto and Kilinga Handeni

Morogoro: Kisitwi, Kihunza, Mngazi and Uluguru mts.



OPAL BACKGROUND

Opal Name History: Opal is the most colorful of gems. Its splendid play of color is

unsurpassed, and fine examples can even be more valuable than Diamond. The play of

color consists of iridescent color flashes that change with the angle at which the stone

is viewed. This phenomenon is often called opalescence. The play of color may consist

of large, individual flashes of color (known as schillers), or may be of tiny, dense

flashes. The intensity and distribution of the color flashes is a determining factor in

the value of an Opal.

Color Ranges: White, Colorless, Blue, Red, Green, Yellow, Orange, Brown, Pink,

Purple, Gray, Black, Banded, and Multicolored.

TYPES OF OPAL:

Opals are classified into two types; Precious Opal and Common Opal.

Opals displaying play of color are known as Precious Opals, and opals lacking play of

color are known as Common Opals.

Varieties of Opal: There are many varieties of both precious and common Opals.

Black Opal: Is the most desired and beautiful form of opal. It is opal with a dark blue,

dark green or black background with a strong play of color.


White Opal: Opal with a light colored body color (white, yellow, cream, etc.) with

strong play of color.

Fire Opal: Opal with a transparent to translucent deep-orange red. Mostly fire opal

does not show play of color. If Fire Opal displays play of color, it is then called

Precious Fire Opal.

Opal Doublets and Triplets

Opal Doublets: Are thin slices of precious opal glued onto a base with any material to

increase hardness of opal.

Black layer glued onto a base.

Opal Triplets: Are like opal doublets but coated with a thin layer or dome of clear

Quartz on top of cabochon to make them more resistant to scratches. (Glued on

bottom and on Top covered with thin layer of other transparent materials)

Black layer onto a base and thin transparent on top glued


Crazing Problem: A condition whereby opal shows cracks internally or on the surface

when opal loose moisture. It is advised to keep opal away from excessive temperature.

But not all opals are affected by crazing.


Refractive Index (RI): SR 1.450 Specific gravity (SG): 2.15 Inclusion: patches or dots of play of color. The pattern maybe in terms of small dots

(pin fire), large patches (flash) or distinct patches known as harlequin.


SYNTHETICS:

Gilson synthetic opal or other synthetic opal, under magnification they show

snakeskin-like structure or known as chicken wire pattern. Synthetic opal also can

show columnar structure vertically.

OPAL DEPOSIT IN TANZANIA

Kigoma: Buhoro, Nyakitonto and Makere


MALACHITE BACKGROUND

Malachite Name History: The stone's name derives from Greek molochitis lithos,

"mallow-green stone”. The mineral was given this name due to its resemblance to the

leaves of the Mallow plant.

Color Ranges: green, bluish-green or greenish blue with bands


Refractive Index (RI): AGG 1.655 to OTL (use birefringence blink method) Specific gravity (SG): 3.95 Inclusion: distinctive green banded appearance


SYNTHETICS/SIMULANTS/IMITATION/

Imitation: Glass, plastic

Confuse with: Turquoise, Jadeite, Nephrite

MALACHITE DEPOSITS IN TANZANIA

Dodoma: Winza

Rukwa: Mpanda

Mara: Kamba Hill Tarime

Mtwara: Masasi Ntaka


FLUORITE BACKGROUND

luorite Name History: Latin meaning flow.

Color Ranges: It ranges from yellow, green, blue and purple. Purple or blue are mostly

banded with colorless bands.


Refractive Index (RI): SR 1.43 Specific gravity (SG): 3.18 NET Inclusion: Color Zoning or Bands, it might be also parti-colored, all inclusions


Confuse with: Since fluorite has every color, it confuse with any gemstone.

FLUORITE DEPOSITS IN TANZANIA

Mbeya: Chunya, Tukuyu

Rukwa: Mpanda

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MOONSTONE BACKGROUND

oonstone Name History: It is called moonstone because it has a white

shimmer like moonshine. That optic effect is called adularescence. It can

also show asterism (star effect)

Color Ranges: It is colorless to white with a whitish-silvery to bluish sheen called

adularescence (bluish sheen against colorless body.)But can be orange, yellow or

brown.

Varieties: There are two moonstone varieties, Moonstone Orthoclase and Moonstone

Labradorite

Moonstone Orthoclase – blue sheen with colorless body while

Moonstone Labradorite – sometime called rainbow moonstone, it has strong blue or

multi-color sheen.


Refractive Index (RI): DR/AGG 1.518 to 1.526 Specific gravity (SG): 2.58 Inclusion: centipede like inclusions


Confuse With: Blue chalcedony and glass imitation

MOONSTONE DEPOSITS IN TANZANIA

Morogoro: Kilosa Gairo

Dodoma: Mkoyo and Zoisa Kondoa

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SUNSTONE BACKGROUND

Sunstone Name History: The name refers to the color and glitteriest of the

gemstone which look-like the sun.

Color ranges: The sunstone has different varieties but the common one is

orange.


Refractive Index (RI): DR/AGG 1.539 to 1.547 (sunstone Oligoclase) 1.518 to 1.526 (sunstone Orthoclase) Specific gravity (SG): 2.65/2.58 (sunstone Oligoclase/ sunstone Orthoclase) Inclusion: Reddish to Golden metallic platelets


Varieties: There are two varieties of Sunstone. Sunstone Oligoclase and Sunstone

Orthoclase

Confuse with: Glass imitation, Plastic imitation

SUNSTONE DEPOSIT IN TANZANIA

Morogoro: Mtimbila Mahenge and Kilosa Gairo

Tanga: Mtae Hill Lushoto

Kilimanjaro: Ugweno Mwanga


AMAZONITE BACKGROUND

mazonite Name History : comes from amazone forest where it is believed

to be mined for the first time commercially.

Color Ranges : Green to Greenish- blue


Refractive Index (RI): AGG 1.522 to 1.530 Specific gravity (SG): 2.56 to 2.58 Inclusion: mottled coloring with grid-like patterns


Confuse with: Chalcedony, Chrysoprase, Serpentine and Turquoise

AMAZONITE DEPOSITS IN TANZANIA

Tanga : Luguruni handeni

Morogoro : Kilosa Gairo

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LABRADORITE BACKGROUND

Labradorite Name History: It was first discovered in Labrador, Canada and named

after that area.

Color Ranges: Labradorite is a member of the Feldspar family with remarkable play of

color, known as Labradorescence. The color usually ranges from gray-green, dark

gray, black or grayish-white. Labradorite is composed in aggregate layers that refract

light as iridescent flashes of peacock blue, gold, pale green or coppery red. The

predominant blue varies within the light, displaying hues from deepest blue to various

shades of pale, almost blue-green.


Refractive Index (RI): AGG/DR 1.559 to 1.568 Specific gravity (SG): 2.70 Inclusion: Black-needle like inclusions, metallic looking platelets which cause

Labradorescence and repeated twinning.


Confuse with: Rainbow moonstone

LABRADORITE DEPOSITS IN TANZANIA

Kigoma: Kidahwe, Nyakitonto


QUARTZ BACKGROUND

Quartz is among abundant gemstones on earth. The abundance of quartz is due to its

formation, it is made by silica and oxygen (silicate oxide - SiO2). Since silica and

oxygen are found everywhere on earth, quartz is also found everywhere.

The formation of quartz varieties depends on the size of the silica (clay) which

combines with oxygen in presence of favorable temperature and water. The silicate

crystallizes either in macro or micro depending on the silica size. Therefore, quartz

varieties are divided into two groups; Macro – crystalline quartz and Micro – crystalline

quartz.

NB: All quartz varieties are Uniaxial positive; Might show a bull’s eye or Airy’s spiral optic figure.

Quartz also shows brazil-law twinning under crossed polarizing filters.

Macro- Crystalline Quartz Micro – Crystalline Quartz

Rose quartz, Chalcedony ;

Citrine Chrysoprase

Amethyst Chrysocolla-in- chalcedony

Rock Crystal Onyx, Carnelian

Smoky quarts Agate ,Iris agate, Fire agate, Dendritic agate

Aventurine quartz Bloodstone

Jasper


ROSE QUARTZ BACKGROUND

Name History: It is called rose quartz simply because, the color looks like rose flower.

Color Ranges: The color of rose quartz ranges from very light to medium dark pink.


Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: look cloudy due to fracture, never transparent (semitransparent to

translucent)



Imitation: Glass and Plastic

Alternatives: Topaz, Spinel, Tourmaline, Ruby.

ROSE QUARTZ DEPOSITS IN TANZANIA

Kigoma: Mbirira Kasulu



CITRINE QUARTZ BACKGROUND

itrine Name History: The name citrine is related to citrus fruit’s color.

Color Ranges: The color of citrine ranges from light golden yellow to reddish yellow.

Most people confuse citrine with topaz of similar color.


Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: Color zoning, negative crystals, two and three phase inclusion, twinning



Imitation: Glass and Plastic

Synthetics: Synthetic hydrothermal quartz, Synthetic sapphire, Synthetic Spinel

Confuse with: Topaz, Spessartite, Orange Sapphire, Carnelian, Amber, Chrysoberyl,

and Tourmaline.

CITRINE QUARTZ DEPOSITS IN TANZANIA

Morogoro: Rubeho Kilosa


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AMETHYST QUARTZ BACKGROUND

methyst Name History: No vivid information about amethyst name.

Color Ranges: The Amethyst color is purple. The finest amethyst color comes from

Africa.


Refractive Index (RI): SR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion Negative crystals, liquid, color zoning, two and three phase.



Imitation: Glass, Purple synthetic corundum, Synthetic Spinel triplets

Synthetics: Hydrothermal

Confuse with: Topaz, Spinel, Tanzanite, Sapphire, Tourmaline, Iolite, Rhodolite

garnet.

AMETHYST QUARTZ DEPOSITS IN TANZANIA


Morogoro: Rubeho Kilosa and Tungi


A


ROCKY CRYSTAL QUARTZ

ocky Crystal Name History: It is called rocky crystal because it looks like colorless

crystal. The colorless, transparent variety of Quartz, free of any impurities, is known

as "Rock Crystal". Flawless and very large cuts may be cut from Rock Crystal.

Color Ranges: It is colorless quartz.

Name History: The name citrine is related to citrus fruit’s color.

Color Ranges: The color of citrine ranges from light golden yellow to reddish yellow.

Most people confuse citrine with topaz of similar color.


Refractive Index (RI): DR 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: needles, two and three phase inclusions, liquid crystals.



-No information at present

ROCKY CRYSTAL QUARTZ DEPOSITS IN TANZANIA

Morogoro: Rubeho Kilosa



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SMOKY QUARTZ BACKGROUND

Smoky Quartz Name History: Smoky Quartz is the brown "smoky" variety of

Quartz. It ranges in color from light brown to black.

Color Ranges: It ranges in color from light brown to black.


Refractive Index (RI): 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: crystals, two and three phase inclusion, needles,




SMOKY QUARTZ DEPOSITS IN TANZANIA

Quartz is one of the most common and varied minerals on earth, and its abundant throughout

the country. Quartz is extremely common and is found in numerous localities throughout the

world.


AVENTURINE QUARTZ BACKGROUND

venturine Quartz Name History: The name reflects the phenomenon effect caused

by chrome mica inclusions which cause appearance of glittering spots of color-

Aventurescence.

Color Ranges: It is almost green but rarely yellow, gray and brown.


Refractive Index (RI): 1.544 to 1.553 Specific gravity (SG): 2.66 Inclusion: chrome mica inclusions (tiny, disk-like, flakes or platelets randomly

distributed) which cause Aventurescence phenomenon.




AVENTURINE QUARTZ DEPOSITS IN TANZANIA

Quartz is one of the most common and varied minerals on earth, and its abundant

throughout the country. Quartz is extremely common and is found in numerous

localities throughout the world.

A


CHRYSOPRASE BACKGROUND

hrysoprase Name History: the name comes from Greek language, meaning gold

leek.

Color Ranges: It is almost yellowish green.


Refractive Index (RI): AGG 1.530 to 1.540 Specific gravity (SG): 2.60 Inclusion: Not diagnostic




CHRYSOPRASE DEPOSITS IN TANZANIA

Dodoma: Chamwino, Itiso-Haneti

C


CHALCEDONY VARIETIES BACKGROUND


Refractive Index (RI): 1.530 to 1.540 Specific gravity (SG): 2.5 to 2.6

Inclusion: curved, straight bands or layers.


CHALCEDONY DEPOSITS IN TANZANIA:

Dodoma: Haneti – Itiso Hill.

Kigoma: Kasulu.


AGATE BACKGROUND

Color Ranges: All colors banded with curved or straight lines.

Varieties: moss agate, fire agate, dendritic agate, iris agate

FIRE AGATE

Refractive index (RI): AGG 1.53 to 1.54 Specific Gravity (SG): 2.60


DENDRITIC AGATE


IRIS AGATE


MOSS AGATE



ONYX

Refractive index (RI): AGG 1.53 to 1.54

Specific Gravity (SG): 2.60

SARD

Refractive index (RI): AGG 1.53 to 1.54

Specific Gravity (SG): 2.60

SARDONYX



CARNELIAN


CHRYSOCOLLA - IN - CHALCEDONY


JASPER BACKGROUND



BLOODSTONE



PEARL BACKGROUND

earls are among the most ancient decorations used by human being.

Natural Pearl - Pearl that is formed from calcium carbonate secretions that forms naturally within a mollusk without any human intervention. This term is distinguished from the more common Cultured Pearls which are produced with human intervention.

Cultured Pearl. Cultured Pearls are produced by inserting a foreign substance known

as a nucleus within the body of an oyster or mussel, which in turn causes the

organism to grow a pearl around the nucleus. Oysters are cultivated and harvested in

mass numbers for the purpose of growing Pearls within them. Almost all Pearls

currently available on the gemstone market are of Cultured Pearl.

VARIETY OF PEARLS.

Freshwater Pearl - Pearl that grew in a non-saline environment in a freshwater mussel with a habit of forming in irregular “potato” like shapes. The most abundant form of Pearls because each mussel can produces up to 50 Pearl while saltwater oysters produce only one to three Pearls per oyster.

Saltwater Pearl - Pearl produced by a mollusk such as an oyster in a body of saltwater such as the ocean.

Akoya Pearl: Cultured Pearls with a white color and a consistent round shape and a

mirror- like metallic luster. Sometimes are treated to look black or a very dark blue.

South Sea Pearls: Pearls with large size, white and golden color

Tahitian Pearl: Also known as “Black Pearl.” They range in color from green to blue,

red, gold and black.

Abalone Pearl These pearls are often an iridescent blue color and commonly horn-shaped

P

http://www.minerals.net/mineral-variety/Gemstone/Abalone_Pearl.aspx


Overtone: Although Pearls are characterized by body color, they also have an

“overtone.” Overtone is the word used to describe the glint of a Pearl in various

lighting. Overtones are most apparent in saltwater pearls. Although Freshwater pearls

have an overtone, it is not as prominent or exact as those found in saltwater pearls.

PEARLS DEPOSITS IN TANZANIA

Along the Indian Ocean in Mainland and Zanzibar


RARE BLUE STONES THAT LOOK LIKE

LAPIS LAZULI

Lapis Lazuli is a deep blue opaque gemstone with pyrite sparkling.


SODALITE

White streak/ irregular white lines



SUGILITE


CHAROITE


AZURITE



Reference

1. GIA Lab Manual

2. Gemstones of the World By Walter Schumann

3. GIA Gem Reference Guide

4. Gemstones Guide by Shazmin,2000

5. Gems Picture credits: Google gemstones picture

6. Gemstones Processing Steps by Eng. Gilay Shamika,2010

7. http://www. Minerals.net

8. http://www.realgems.org

9. http://www.gst.go.tz

10. http:// www.tmaa.go.tz

11. Philosophy of Gems Business by Eng.Gilay Shamika,2013

http://www.realgems.org/

Gemstones of Tanzania by Gilay Shamika

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Transcript of Gemstones of Tanzania by Gilay Shamika