Biblical Reference

The leaders brought onyx stones and other gems to be mounted on the ephod and breastpiece.

Exodus 35:27

What is a Mineral?• A mineral is a naturally formed solid

substance with a crystal structure

Definition of a Mineral

What do all Minerals have in Common?

Minerals:• Are formed by Natural Processes• Are not Alive and Never Were Alive• Have a Definite Volume & Shape• Are Elements or Compounds with a Unique

Chemical Make-Up• Are Crystals (particles arranged in patterns

that are repeated over and over)

How do Minerals Form?• Cooling of Magma

– Fast Cooling = No Crystals (Mineraloids)– Medium Cooling = Small Crystals– Slow Cooling = Large Crystals

How do Minerals Form?• Elements dissolve in liquid (usually water).• Minerals form when the liquid evaporates.

– Example: Halite forms when salt water evaporates.

Identifying Minerals• Physical Properties are

used to identify minerals.

– Some properties are more useful then others in mineral identification.

– Rarely is one physical property enough to identify a mineral.

Characteristics of Minerals

Physical Properties Used to ID Minerals

–Color–Streak–Luster – metallic, non-metallic –Mohs Hardness Scale (1-10)–Specific Gravity–Cleavage and Fracture–Crystal Form

Color• Least Useful – Can be misleading due to

impurities.

– One mineral can have various colors.

– More than one mineral can be the same color.

All of these crystals are Quartz!

A Sample of White Minerals

Talc

Quartz

Feldspar

Calcite Gypsum

Streak• Streak is the color of a mineral in powder

form.

– The powder forms when the mineral is rubbed against a rough surface, such as an unglazed ceramic tile.

• Some minerals have a distinct streak color, however most leave a clear streak.

• Streak is more reliable than color alone, because each mineral leaves the same colored streak regardless of the mineral’s color

Streak• All varieties of Hematite all have the same

streak.

Luster• The way in which a mineral reflects light is its

luster.• There are two types of luster:

– Metallic:• Minerals shine like polished metal.

– Nonmetallic• Minerals don’t shine like polished metal, and are

sometimes described as glassy, pearly, dull and earthy.

Metallic Luster Examples

Non-Metallic Luster Examples

Mohs Hardness Scale• Hardness is a measure of a minerals

resistance to being scratched.

• This is one of the methods to identify a mineral.

• It also determines how quickly a mineral is broken up by weathering.

Mohs Hardness Scale1 (Talc) = Softest 10 (Diamond) = Hardest

Mohs Hardness Scale• Test more than one area of each sample• Fingernail: Hardness less than 2• Glass: Hardness = 5.5• If you can make a scratch in the mineral with

your fingernail:– Hardness < 2.

• If you cannot make a scratch in the mineral with your fingernail, but the mineral cannot make a scratch in the glass:– 2 < Hardness < 5.5

• If the mineral scratches the glass:– Hardness > 5.5

Friedrich Mohs

Specific Gravity• Specific Gravity is the ratio of the mass of a

substance to the mass of an equal volume of water at 4 C.– Imagine there are equal volumes of material

present in each of the following bottles:

1) a gallon bottle filled with water2) a gallon bottle filled with feathers3) a gallon bottle filled with lead– Arranging them in order of increasing specific gravity

would yield: feathers, water, lead

Mineral Specific Gravity

Cleavage• Atomic arrangement determine the way the

mineral breaks.

• Cleavage is the tendency of a mineral to split along flat surfaces, or planes of cleavage.

• Cleavage can occur in one or more planes.

• Cleavage is caused when weak bonds in the crystal structure of a mineral are split apart.

Cleavage: Sheets• Mica cleaves in thin sheets, because the

weakest joints are between flat sheets of strongly-joined atoms.

Cleavage: 2 Directions• Orthoclase is the classic example of

cleavage in 2 directions.

Cleavage: Cubes• Galena and Halite cleaves into cubes (three-

dimensional), because the joints inside are equally strong.

Fracture• Other minerals break unevenly along rough

surfaces, called fracture.

• These minerals do not break along nice flat planar surfaces.

– The “nugget” shape of gold is a good representation of random fracture.

Crystals• A crystal is a regular geometric solid.

• The arrangement of atoms determines the shape of the crystal.– Halite atoms arrange in a pattern which causes a

cube shape.

Crystals• Quartz forms in 6 sided crystals because of

its atomic arrangement.

Other Crystal Shapes

Trigonal - rhombohedral

Special PropertiesSome minerals display unique properties, such as:

- Magnetism

- Bubbling in Acid

- Double Refraction

- Polarization

- Magnification

- Fluorescence

- Radioactivity

Special Properties• Magnetite and Lodestone are magnetic.

Radioactivity• Uranium gives off subatomic particles and it

is used in making nuclear weapons and for medical research.

Fluorescence and Phosphorescence

• Fluorescent minerals glow under ultraviolet light.

• Phosphorescent minerals continue to glow after the light is removed.

Other Physical Properties

• Smell– Sulfides smell like a struck match or rotten eggs– Arsenic smells like garlic

• Taste– Halite and Hanksite are salty– Sylvite is bitter

• Texture– Fluorite has a smooth texture– Talc is greasy

Groups of Minerals• About 1,500 unique minerals have been

identified• Geologists have classified minerals into

groups– Distinct Chemical Nature– Specific Characteristics

Silicates• Most abundant group

• Contain Silicon and Oxygen

• Strongly-bonded Tetrahedron Ions

Carbonates• Composed of one or more metallic elements

combined with a Carbonate (CO3-)

• Typically transparent and lightly colored

• A common component of the earth’s inner crust

Calcite Rhodochrosite

Oxides• Compounds of Oxygen and a Metal

• Strong Chemical Bond – Very Hard and Dense

• Great sources of iron and rare metals

Sulfides• Sulfur and a Metallic Ion

• Highly symmetric, simple structures

• Low Hardness and High Specific Gravity

Galena Pyrite

Sulfates• Composed of Elements with a Sulfate Ion (SO4

2-)

• Delicate and occur near the earth’s surface

Barite Gypsum

Native Elements• Made up of a Single Element

• Highly Ordered Atomic Arrangement

Copper Gold

Mineral Classification

Cecelia Payne

Ores• A mineral is an ore if it contains a valuable

substance and can be mined at a profit.

– The classification of a mineral as an ore can change depending upon the supply and demand.

• Ores deep within Earth’s crust are removed by underground mining, while ores near Earth’s surface are obtained from large open-pit mines.

What is a Gem?• A gem is a mineral or rock that has value

– Usually rare

• Example:– Mineral: Corundum– Gem: Ruby

Mineral Uses – Building a House

Mineral Uses – In the Kitchen

Mineral Uses – Transportation

Mineral Uses – Medical/Dental

Which property causes the mineral galena to break into tiny cubes?

Pop Quiz

A. crystal structure B. density C. hardness D. luster

A. color

B. streak

C. luster

D. crystal structure

Dull, silky, waxy, pearly and earthy are terms that best describe which property of minerals?

Pop Quiz

Which of the following is a true statement about Mohs Hardness Scale?

Pop Quiz

A. Diamond is represented by a 1, and Talc is represented by a 10.

B. Talc is represented by a 1, and Diamond is represented by a 10.

C. Calcite is represented by a 1, and Quartz is represented by a 10.

D. Quartz is represented by a 1, and Calcite is represented by at 10.