Minerals

Chapter 2

Mineral: a naturally occurring substance formed

in the Earth• Inorganic• Solid substance

• Definite chemical composition

How Minerals Form1. Crystallization from magma

2. Precipitation

3. Pressure and temperature

4. Hydrothermal solutions

Mineral GroupsCan be classified based on their composition1. Silicates• Silicon and oxygen combine to form a structure

called the silicon-oxygen tetrahedron.

2. Carbonates• Minerals that contain the elements carbon, oxygen,

and one or more other metallic elements

3. Oxides• Minerals that contain oxygen and one or more other

elements, which are usually metals

Mineral Groups4. Sulfates and Sulfides• Minerals that contain the element sulfur

5. Halides• Minerals that contain a halogen ion plus one

or more other elements

6. Native elements• Minerals that exist in relatively pure form

Over 2,000 are known!

Identifying Minerals: 1. Color

• Most easily observed property

• Yet, least useful property

Identifying Minerals: ColorWhy it is the least useful property…

• Different minerals have the same color

• One mineral can have different colors

• Impurities can alter color• Some change color when exposed to

air• Light can distort color

Identifying Minerals: 2. Luster

•Way a mineral shines

Identifying Minerals: Luster

Metallic: shines like polished metal

Pyrite“Fool’sGold”

Identifying Minerals: Luster

Nonmetallic: does not shine like metal

Identifying Minerals: Luster

Pearlylike a pearl

Talc

Identifying Minerals: Luster

Greasy

Turquoise

Identifying Minerals: Luster

Vitreouslike

shining glass

Amethyst

Identifying Minerals: Luster

Resinous

like wax

Identifying Minerals: Luster

Dull or Earthy

Bauxite

Identifying Minerals: 3. Crystal Shape

•The shape of a crystal results from the way the atoms of a mineral come together as the mineral forms

Identifying Minerals: 4. Streak Test

•Color of a mineral’s powder form

•Usually, streak is not the same color as the mineral

•Streak doesn’t vary

•Metallic mineral has dark streak

•Nonmetallic – colorless or light streak

Identifying Minerals: Streak Test

Identifying Minerals: 5. Cleavage

• The splitting of a mineral along certain flat surfaces

• Related to the types of bonds in the internal structure of the mineral

Identifying Minerals: Cleavage

Mica Has Cleavage in One Direction

Identifying Minerals: 6. Fracture

• the way a mineral tends to break –unevenly!!!

Identifying Minerals: Fracture

jaggedSplintery

Identifying Minerals: 7. Hardness

•Resistance to being scratched

•Moh’s hardness scale

• Mohs Scale,

identified numerically by standard

minerals, from 1

(softest) to 10 (hardest):

• 1. Talc • 2. Gypsum • 3. Calcite • 4. Fluorite • 5. Apatite • 6. Orthoclase • 7. Quartz • 8. Topaz • 9. Corundum • 10. Diamond

The Geologist Can Find An Ordinary Quartz, (that) Tourists Call

Diamond!

To remember the Mohs scale try remembering this

phrase:

• You typically do not carry around a supply of the 10 minerals on the hardness scale. However, you can use the following items to help estimate the hardness of a mineral:

Tools for Testing Hardness

Tools for Testing Hardness

• finger nail (H = 2.5)• penny (H = 3.5)• common nail (H = 4.5)• glass plate (H = 5.5)

Identifying Minerals: Special Properties

•Acid test

http://www.westhamptonbeach.k12.ny.us/Teachers/Cohen/sciweb/earthscience/sedimentary/Mvc-327w.mpg

Identifying Minerals: Special Properties

•Magnetic test

Identifying Minerals: Special Properties

•Taste test

Some minerals have a distinct taste. Never do this test after the acid test!

Quartz

Feldspar

Mica

Talc

Amphiboles

Galena

Halite

Biotite

Calcite

Hematite

Pyrite

Magnitie

Olivine

Garnets