Minerals• Mineral- A naturally occurring, inorganic

solid that has a definite chemical composition and crystal structure

• All minerals must:• Occur naturally in/on the Earth• Be inorganic (not formed from living things or the

remains of living things)• Be a solid• Have a definite chemical composition• Have a characteristic crystal structure

• There are about 2500 different kinds of minerals

Identifying Minerals

• Minerals have certain physical properties that can be used to identify them

• Some properties can be observed just by looking at the mineral

• Color• Luster• Crystal shape• How it breaks

• Certain properties can only be determined by testing• Hardness• Streak• Specific Gravity• Acid test

Mineral Color• The color of a mineral often helps to identify

it, but very few minerals can be identified by color alone

• Why?

– Many minerals have similar colors

– Impurities can produce different colors

– Some minerals change color due to exposure

Mineral Luster• Luster- Describes the way a mineral

reflects light from its surface• All minerals have either a metallic or

nonmetallic luster

•Metallic luster- When a mineral looks and/or shines like a metal (ex.- pyrite)•Nonmetallic luster- when a mineral doesn't reflect light or look like a metal (7 types)

Nonmetallic Mineral Lusters

1. Vitreous or Glassy- Quartz

2. Pearly- Mica

3. Resinous or Waxy- Sphalerite

4. Silky- Asbestos

5. Adamantine (hard or unbreakable)- Diamond

6. Greasy or Oily- Talc

7. Dull or Earthy- Sulfur

Crystal Shape• All minerals have a characteristic crystal

shape that results from the way atoms or molecules come together when the mineral is forming

• The conditions in which the mineral formed, may make it difficult to determine its crystal shape (crystals need room and time to develop)

• Crystal- Solid in which the atoms or molecules are arranged in definite repeating patterns

Crystal Systems All minerals have internal atomic patterns in one of 6 possible

crystal systems

Crystal System ExamplesCubic Fluorite Halite

Tetragonal Wulfenite Zircon

Orthorhombic Sulfur Topaz

Monoclinic Malachite Orthoclase feldspar

Triclinic Amazonite Plagioclase feldspar

Hexagonal Quartz Tourmaline

Crystal Systems

Halite

ZirconQuartz

Staurolite

Gypsum

Rhodonite

Cleavage & FractureThe way a mineral breaks can be used in its identification

(related to the mineral’s internal arrangement of atoms)

•Cleavage- The tendency of a mineral to split along smooth, definite surfaces

•Cleavage planes may meet at angles that form geometric patterns similar to crystal shapes

Cleavage & Fracture

• Fracture- When a mineral breaks along a rough or jagged surface

• Types of fracture:1. Conchoidal or shell-like- Smooth

curved surface, like the inside of a clam shell

(ex.- Obsidian)

2. Fibrous or splintery- Jagged surface with

sharp uneven edges (ex.- Copper)

3. Uneven or irregular- Surface is generally rough

all over (ex.- serpentine)

Mineral Hardness• Hardness- The ability of a

mineral to resist being scratched

• Mohs’ scale- A reference guide for determining the hardness of minerals that uses ten minerals arranged in order of increasing hardness

The Girls Came From All Over Quebec To Collect Diamonds

Determining the Hardness of a Mineral

To determine the hardness of an unknown mineral:1. Rub the mineral against the surface of a mineral (or other

substance) that you know the hardness of2. If the unknown mineral scratches the known mineral, it is

harder than the known mineral3. If the unknown mineral is scratched by the other mineral,

then it is softer than that mineral 4. If neither mineral scratches the other, they have the same

hardness5. Based upon the scratch test, minerals are assigned a

number between 1 and 10 (with .5 increments)

Streak• Streak- The color of a mineral in its

powdered form– Produced when a mineral is rubbed against a

hard, rough surface– Usually a piece of unglazed porcelain known as a

streak plate• Even though the color of a mineral may vary,

its streak does not• For many minerals, its color and the color of its streak may be different

Specific Gravity• Specific Gravity- The ratio of the weight of a mineral to the weight of an

equal volume of water

– Tells you how many times as heavy as water a mineral is

– To Calculate:

Specific gravity = Wt. of mineral in air Wt. of an equal volume of water

OR

Specific gravity = Wt. of mineral in air Loss of wt. in water

– Typical Specific Gravities:• Nonmetallic minerals- less than 3• Metallic minerals- about 5• Pure gold- 19.3

The Acid Test• Some minerals fizz or bubble when

hydrochloric acid (HCl) is dropped on them– The HCl reacts with the mineral and

produces carbon dioxide (CO2) gas

– Can be used to identify calcite, copper, and other carbonate minerals

Special Properties of Minerals

1. Magnetism- Magnetite

2. Taste- Halite (Rock Salt)

3. Fluorescence (Glows under UV light)- Scheelite and some Calcites

4. Phosphorescence (Glows without UV light)- Sphalerite

5. Radioactivity- Uranium

6. Double refraction (Splits light rays into two parts, causing double vision)- Calcite

7. Smell- Sulfur

From Minerals to Rocks

• “Minerals are to rocks as letters are to words” (Quote from Professor R. Lingner, WSC)

• Rocks- Hard substances composed of one or more minerals

• Usually made of more than one type of mineral • May contain naturally occurring substances

that would not be considered a mineral• Are grouped according to how they form as

either igneous, sedimentary, or metamorphic