*What is a Mineral?*

Naturally occurring Inorganic Solid Definite crystalline structure

* = Most Important information

*Mineral characteristics*

*Naturally formed *No substance created in a lab can be a mineral. examples: plastic, steel, sugar, paper

• *Inorganic– *Not living

• *Solid– *Liquids and gases are not minerals. examples: water, petroleum, lava, oxygen

*Mineral characteristics*

Characteristic *crystalline structure *must have an ordered arrangement of atoms *displays repetitive geometric patterns in 3-D

glass not a mineral (no internal crystalline structure)

• Definite *chemical composition– *must have consistent chemical formulaexamples: gold (Au), quartz (SiO2), orthoclase (KAlSi3O8)

basalt (like many other rocks) contains variable ratios of different minerals; thus, has no consistent formula

Mineral StructureCrystals: solids with atoms arranged in orderly, repeating patterns.

*Some crystals form from magma, hot melted rock below the Earth’s surface.

*When magma cools slowly, crystals are large.

*When magma cools quickly, crystals are small.

GRANITE ROCK

*Minerals are the building blocks of rocks

Mineral Structure

*Contain one or more elements which are made of atoms

*Most made of compounds of several elements (Quartz SiO2)

Identifying Minerals

*Six main properties: Color Luster Streak Cleavage or Fracture Hardness Density/specific gravity

We will be testing these properties in class during our mineral ID lab.

Identifying Minerals

*Color: Most obvious, but often misleading Many minerals have same/similar color Different colors may result from impurities

Example:Quartz

Identifying Minerals

Luster: *How a mineral surface reflects light (shines) Two major types:

Metallic luster Non-metallic luster

Metallicexample:Galena

Non-metallicexample:

Orthoclase

There are several terms used to describe nonmetallic luster.

Examples could be vitreous, like the quartz on the left, or pearly,

like the gypsum on the right.

Other terms that might be used include greasy, dull, and earthy.

Can you tell which of these has an earthy luster and which has a

vitreous luster?

Earthy

Vitreous

Identifying Minerals

Streak: *Streak – color of a mineral in powdered form

(used for metallic minerals)

Obtained by scratching a mineral on a piece of unglazed porcelain.

Example:Hematite

The streak is often not the same color as the mineral.

A minerals color may vary, but the streak rarely will!

*Identifying Minerals*

Cleavage vs. Fracture: *The way a mineral breaks– Cleavage: tendency of a mineral to break

along planes of weakness (smooth)

– Minerals that do not exhibit cleavage are said to fracture (uneven)

*Minerals with cleavage break along smooth, flat surfaces.

Physical Properties of Minerals *Fracture:

minerals that do not exhibit cleavage are said to fracture

*minerals with fracture break with uneven, rough, or jagged surfaces

Identifying Minerals

Hardness: *How easy it is to scratch a mineral Mohs Scale of Hardness

relative scale consists of 10 minerals, ranked 1 (softest)

to 10 (hardest)

Mohs Scale of Hardness

Hardest (10) – Diamond

Softest (1) – Talc

Common objects:

- Fingernail (2.5) - Copper penny (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5)

Identifying Minerals Specific gravity: *weight of a mineral divided by weight of an

equal volume of water metallic minerals tend to have higher specific

gravity than non-metallic minerals

GalenaSG=7.5

QuartzSG=2.67

Specific Gravity/Density

=

*Density – how much matter is in something (Density=mass/volume)