5.4Mineral GroupsObjectives1) Describe the properties of the most common minerals (silicates

and carbonates).2) Describe tests used to identify mineral groups.

Major Silicates

90+% of the minerals in Earth’s crust are members of the silicate family

Silicate: a compound of silicon, oxygen, and usually one or more metallic elements Basic building block is

the silica tetrahedron Classified by the ways

the tetrahedra are linked together

Quartz

Second most abundant mineral in the Earth’s crust

Made entirely of tightly bound silica tetrahedra

Chemical name: silicon dioxide 2 oxygen atoms per

silicon atom

Quartz cont’d

Looks: Glassy or greasy luster Pure quartz = colorless or

white Other colors = rose,

amethyst (purple), smoky

Fracture: Conchoidal or irregular

Hardness: 7 on the Mohs scale

Common property used to identify it

Hardest of the common minerals

Quartz cont’d

Hardness and how it looks: Make it ideal for certain

uses Watch movements Prisms Heat lamps Lenses Glass Paints Jewelry

Quartz cont’d

Found in granite

Important part of many other types of rocks Most sands are made

mainly of quartz

Feldspars

Makes up 60% of Earth’s crust

Share 3 features 2 directions of cleavage Hardness of 6 Pearly luster

Made of aluminum, oxygen, and silicon atoms Creates a net electrical

charge Balanced by the addition of

other metals Potassium Sodium calcium

Feldspars cont’d

2 major groups Potassium feldspars

Most common is orthoclase Light-colored pink

or salmon 2 cleavage

surfaces meet at right angles

Most commonly found in granite

Feldspars cont’d

Sodium-calcium feldspars Plagioclase

Albite and labradorite

Range in color from white to gray

2 cleavage surfaces meet at slightly less than a right angle One cleavage

surface is often marked by fine parallel lines (striations)

Feldspars cont’d

Important rock-forming minerals

Important economically Manufacture of glass

and ceramics

Other Silicates

Pyroxene family Occur widely Cleavage surfaces meet

at nearly right angles Common member

augite

Other silicates cont’d

Ferromagnesian silicate Can belong to almost

any of the silicate families

All contain iron and magnesium

Always dark in color Example

Augite 2 good cleavages Hardness 5-6

Other Silicates cont’d

Mica family Soft

Hardness = 2.5 Perfect cleavage

Form flat crystals that cleave in only one direction Makes thin sheets or flakes

Can be easily picked out of rocks Examples

Muscovite (white mica) Silvery white

Biotite Dark brown or black

Used for paints, plastics, rubber, roofing, electronic insulators

Carbonates

Carbonate: a mineral made of negatively charged carbonate ions bonded to positive metal ions 1 carbon atom

covalently bonded to 3 oxygen atoms

Examples Limestone Marble

Carbonates cont’d

More examples Calcite (calcium carbonate)

Most common carbonate mineral

Colorless or white Hardness = 3

Can be scratched with a knife

Bubbles with the acid test Dolomite (calcium magnesium

carbonate) Occurs as coarse or fine

grains in dolomitic limestones Hardness = 3.5-4

Cannot be scratched with a knife

Will not react during an acid test

Oxides and Sulfides

Contain significant amounts of iron

Not as common as silicates or carbonates

Used to make steel, magnets, car parts, medicines, cosmetics, plastics, and paints

Oxides and Sulfides

Oxide: a mineral made of a metal element combined with oxygen

Sulfide: a mineral made of a metal element combined with sulfur

Hematite

Most common iron oxide

Usually red

Earthy luster

Uneven fracture

Some have a silvery metallic luster Gemstones

Leave a red-brown streak on a streak plat

Magnetite

Black iron oxide

Attracted to magnets

Example Lodestone

Natural magnet First compass

needles

Pyrite

Iron sulfide

Most common sulfide mineral

Color Pale brass to golden

yellow

Commonly referred to fool’s gold

5.4 Exit Ticket

1) Describe the properties of the most common minerals (silicates and carbonates).

2) Describe tests used to identify mineral groups.