5.4Mineral Groups Objectives 1) Describe the properties of the most common minerals (silicates and carbonates). 2) Describe tests used to identify mineral groups.
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