Minerals

• A mineral must:1. Occur naturally2. Be a crystalline solid3. Have a definite chemical composition4. Possess characteristic physical

properties5. NOT be organic

Why aren’t the following minerals?

• Water

• Glass

Why aren’t the following minerals?

• Water

– it is a liquid at room temperature

• Glass

– It is not naturally occurring

Why aren’t the following minerals?

• Coal

Why aren’t the following minerals?

• Coal

–It is organic–It lacks a definite chemical composition–It does not have repeating structure

The Most Common Elements in the Earth’s Crust

1. Oxygen2. Silicon3. Aluminum4. Iron5. Calcium6. Sodium7. Potassium8. Magnesium

• These eight elements make up 98.5% of the Earth’s crust.

• Almost 94% of the crust’s volume (not mass) is oxygen.

Elements are not distributed evenly throughout the layers.

Not in your notes.

Not in your notes.

How Minerals Form• Atoms in magma move about. As the

magma cools, movement slows and the atoms move closer together. They bond chemically.

• The rate at which the magma cools determines the size of the mineral grains.

• Dissolved atoms chemically link as water evaporates.

COMMON MINERAL GROUPSThere are seven basic nonsilicate mineral groups.

More than 90% of the minerals in thecrust and mantle are silicates.

1. Native Elements do not combine with other elements in

nature.

Gold (Au)Silver (Ag)Platinum (Pt)Diamond (C)Graphite (C)Sulfur (S)Copper (Cu)

NONSILICATE MINERALS

Copper

Silver

Gold

• The two most abundant elements, silicon and oxygen combine to form the basic building block for most common minerals.

• Four oxygen atoms are packed together around a single silicon atom.

• A silica tetrahedron is the result.

SILICATE MINERALS

Silica tetrahedron

• Half the bonds are ionic.• Half the bonds are

covalent.• It has an overall negative

charge.• Tetrahedrons can link

together in different ways.

Silicates

• Combinations of oxygen and silicon plus one other metallic element are called silicates.

• They can exist independently, or as single chains, double chains, sheets, or frameworks.

Silica Tetrahedron(blue = silicon; brown = oxygen)

4 oxygen anions are bonded to a single silicon cation.

Silicon is positively charged (+4)

Oxygen is negatively charged (-2)

Net charge on tetrahedron: -4Not in your notes.

Single Tetrahedron

• Olivine

Two atoms of magnesium or iron balance the negative charge.

X2SiO4

Single Chain

• Pyroxene

Note the fibrous appearance.

XSiO3

One atom of iron, magnesium, aluminum, or calcium balance the negative charge.

Single Chain Silicates

Adjacent tetrahedrons form a chain by sharing 2 of their oxygen with neighboring tetrahedrons.

E.g. pyroxenes (mafic silicates)Not in your notes.

Double Chain

• Amphibole

XSi8O22(OH)2

A combination of calcium, sodium, iron, magnesium, and aluminum balance the negative charge.

Double Chain Silicates

Two chains can link up by sharing oxygen.

E.g. amphiboles (mafic silicates)

Not in your notes.

Sheet

• Micas– Biotite–Muscovite

KXAlSi3O10(OH)2

A magnesium, iron, and aluminum balance the negative charge in biotite. In muscovite only aluminum balances the negative charge.

Sheet Silicates

Sheets are formed when each tetrahedron shares 3 of its oxygen with neighbors.

E.g. micas, clay minerals

Not in your notes.

Framework

• feldspar

KAlSi3O8 = orthoclase feldspara.k.a. potassium feldspar

Framework Silicates

Every oxygen in each tetrahedron is shared to a form 3-D framework.

E.g. feldspar, quartz (non-mafic silicates)

Not in your notes.

Identifying Minerals

Mineral properties• Colour• Luster• Habit (Shape)• Cleavage & Fracture• Streak• Hardness

Colour:(Not mineral specific)

Quartz comes in a variety of colours

Not in your notes.

Luster:How minerals reflect light

Non-metallic

Metallic

Metallic luster does not have to be shiny – It can look like a broken iron rod.

Mineral Habit (Shape)

Shape a mineral takes if grown unimpeded

Cleavage & FractureCleavage: planes or surfaces of

weakness along which minerals can break

Fracture: surfaces other than cleavage planes along which minerals can break

Examples of Cleavage

Not in your notes.

Cleavage & Fracture and resulting crystal shape

Not in your notes.

Fracture

• Some minerals do not have cleavage but do show a characteristic fracture.

• Fractures (irregular breaks) can sometimes be distinctive

• When the fracture results in smooth, curved surfaces, the sample is said to exhibit “conchoidal” fracture

Quartz has conchoidal fracture

Not in your notes.

Crystalline Structure

• A crystal is a regular geometric solid with smooth surfaces called crystal faces.

• The orderly arrangement of ions determines the shape of the crystal.

• There are six basic crystal shapes

Streak:The powdered form of a mineral when rubbbed on an unglazed tile.

Hardness:Is the resistance of a mineral to abrasion or scratching.

Geologists use Moh’s scale of hardness.

Mohs Mineral Hardness Scale1) Talc

2) Gypsum

3) Calcite

4) Fluorite

5) Apatite

6) Feldspar

7) Quartz

8) Topaz

9) Corundum

10) Diamond

Softest

Hardest

1

2

3

4

5

6

7

8

9

10

If this were an absolute scale diamond would have a value of 40.

As an example, calcite will scratch gypsum and talc but not fluorite, apatite, or any of the others.

The hardest substance also produces the softest substance, graphite.

Other Properties• Specific gravity• Reaction to acid• Striations• Magnetism