Chapter 6

Minerals and Rocks

• Minerals: naturally occurring, inorganic solids, with definite structure and composition; made of one or more elements

– Characteristics of Minerals:• Formed by natural processes• Inorganic (not formed from life processes)• Solid• Definite chemical composition, can have minor

variations (example: salt is NaCl)• Atoms arranged in a pattern

Structure of Minerals: minerals are in the form of crystals (a solid in which the atoms are arranged in repeating patterns)

C. Crystal Systems: Examples of Perfect Crystal Systems

Cubic Tetragonal Hexagonal

Examples: Isometric- Cubic-Halite (salt); Platinum Tetragonal-Zircon; Wulfenite

Hexagonal-Quartz; Corundum

The first group is the ISOMETRIC. This literally means “equal measure” and refers to the equal size of the crystal axes.

CRYSTAL SYSTEMS are divided into 6 main groups.- We will look at 3 groups

Examples:·Gold·Copper·Diamond· Lazurite·Galena· Pyrite

These hexagonal CALCITE crystals nicely show the six sided prisms

HEXAGONAL CRYSTALS

HEXAGONAL Crystal AxesThree horizontal axes meeting at angles of 120o and one perpendicular axis.

a

Examples:·Graphite·Nickeline·Molibdenite·Apatite·Vanadinite· Beryl

Hexagonal Crystals

TETRAGONAL Two equal, horizontal, mutually perpendicular axes Vertical axis is perpendicular to the horizontal axes and is of a different length.

TETRAGONAL CRYSTALS

Examples:· Tourmaline·Dolomite·Hematite·Corundum· Idocrase

Green Tourmaline

Hematite

WULFENITE Same crystal seen edge on.Same crystal seen edge on.

TETRAGONAL CRYSTALS

How Minerals Form:

1.Form from the cooling of hot melted rock (magma); If it cools fast, crystals tend to be small; cools slow, larger crystals tend to form

2. Form from solutions-as liquid evaporates, minerals solidify and form crystals

Major Mineral Groups

Silicates-Made of Silicon, Oxygen, & possibly other element(s); largest group of minerals

Example: Quartz (SiO2)

Carbonates-Made of Carbon, Oxygen, & possibly other elements

Examples: Calcite (CaCO3); Magnetite (MgCO3)

Pink Quartz

Calcite samples

Most Abundant Elements in Earth’s Crust:

1. Oxygen 46.6%2. Silicon 27.7%3. Aluminum 8.1%4. Iron 5%5. Calcium 3.6%6. Sodium 2.8%7. Potassium2.6%8. Magnesium 2.1% ***All other elements make up 1.5% of the Earth’s

crust.

Physical Properties of Minerals:

Hardness-a measure of how easily a mineral can be scratched

***1 is the softest, 10 is the hardest***

Moh’s Scale of Hardness

Sample Element

HardnessCommon

Objects

Talc 1 Fingernail (2.5)Copper penny

(3.5)Iron Nail (4.5)

Glass (5.5)Steel File (6.5)Streak Plate (7)

Gypsum 2

Calcite 3

Fluorite 4

Apatite 5

Feldspar 6

Quartz 7

Topaz 8

Corundum 9

Diamond 10

Gypsum

Apatite

LusterDescribes how light is

reflected from a mineral’s surface– Metallic– Nonmetallic– dull; pearly; silky; glassy;

brilliant; transparent– Waxy– Resinous (looks like

freshly broken shellac)

Color

The color seen when looking at the surface of the mineral; Least reliable property because many minerals can be many colors

Example: Sulfur is pale yellow

Streak The color of the mineral

when it’s broken up in powdered form; Use a porcelain tile to test; Useful for softer minerals; Minerals with a hardness greater than 7 do not leave a streak

Example: Gold has a gray streak

The Way a Mineral Breaks

1. Cleavage-When a mineral breaks along smooth, flat surfaces; Example: Mica

2. Fracture-When minerals break with rough or jagged edges; Example: Quartz

Special Properties Unusual or unique

qualities; Examples: Magnetite is magnetic, Calcite has optical qualities, Jade has a bell-like ring when tapped, Halite has a salty taste, and Sulfur smells like rotten eggs

Uses of Minerals

Gems-Highly prized minerals because they are rare and considered beautiful; the difference in a gem and the common form of a mineral can be slight

Month Birthstone

January Garnet

February Amethyst

March Aquamarine

April Diamond

May Emerald

June Pearl

July Ruby

August Peridot

September Sapphire

October Opal

November Topaz

December Turquoise

Ores-contain useful substances that can be mined for a profit

Examples: Bauxite contains Aluminum

Hematite contains Iron

Sphalerite contains Zinc

Chalcopyrite contains copper

• Strip Mining-Removing ore by digging at Earth’s surface; usually results in a huge pit

• Land Reclamation- mining companies are required to return soil and rock to open pit and cover it with topsoil then plant trees and grass

Asbestos-a mineral with threadlike, flexible fibers used as insulation and as fire protection; has been shown to cause lung diseases including lung cancer

EPA (Environmental Protection Agency)-requires school officials to inspect buildings every six months; flaking asbestos must be removed or sealed over

Minerals can contain other useful elements.

1.Elements must be refined, or purified, from ores

2. Some elements dissolve in fluids, travel through weaknesses in rocks, and in those weaknesses form mineral deposits called vein mineral deposits

3. Titanium is useful element derived from the minerals limonite and rutile

III. Rocks – made of one or more minerals

A. Igneous- form from molten material from a volcano or deep inside Earth; Examples: Obsidian, Granite, & Pumice

B. Sedimentary- Form as a result of processes at or near Earth’s surface; Examples: Halite (rock salt), Limestone, Calcite, & Sandstone

C. Metamorphic- Form from changes due to temperature and pressure increases; can form from all 3 rock types; Examples:

Slate & Marble