Mineral Groups

You can find minerals almost anywhere. Many minerals are

abundant and many have important uses

Minerals are grouped into families according to the elements in them

Silicates

Ninety percent of the minerals in Earth’s crust are silicates

Quartz

• Chemical formula - silicon dioxide• Colorless or white• Hardness of 7• Used in watch movements, prisms, lenses

and jewelry

Feldspars

• Contains silicon, oxygen and aluminum• Makes up 60% of the Earth’s crust• Hardness of 6• Cleavage (quartz doesn’t have cleavage)• Classified into 2 groups: potassium (pink) and sodium

(white or gray) feldspars• Used to make paint

Pyroxene

• Contains silicon, oxygen, iron and magnesium• Cleavage at 90 degrees• Hardness of 5-6

Mica

• Very soft silicates (2.5)• Cleaves into flat sheets• Muscovite – white, contains aluminum• Biotite – black, contains iron• Rock-forming mineral

Carbonates

All members of this family contain carbon and oxygen

Calcite

• Most common carbonate mineral (calcium carbonate)

• Colorless or white• Hardness of 3• Three directions of cleavage• Reacts with hydrochloric acid

Dolomite

Oops…….not this Dolomite

Dolomite

• Contains calcium magnesium carbonate• Hardness of 3.5 – 4• Cleavage (3 directions)• Reacts with hydrochloric acid, but only in powder form

Oxides and Sulfides

Oxides contain oxygen. Sulfides contain sulfur

Hematite

• Most common iron oxide• Uneven fracture • Earthy luster, but some samples have a metallic silver

luster• Hardness of 5-6• Red streak

Magnetite

• Iron oxide• Is magnetic• Hardness of 5.5-6.5• Because of its magnetic properties, magnetite

was used to make the first compass (lodestone)

Pyrite

• Iron sulfide ( a compound containing iron and sulfur)

• Pale brass to golden yellow• Hardness of 6• 6 or 12 sided crystals• Also known as ‘fools gold’