Materials of the Earth Minerals

Minerals are….. Naturally occurring Inorganic Solid Composed of elements or compounds Elements are composed of only one type of atom. Compounds are 2 or more elements chemically combined

Physical Characteristics... Are the result of the arrangement of atoms within the mineral.

Physical Characteristics include... Color Luster Fracture and cleavage Mineral shape (habit) Streak Hardness Specific Gravity

Color Color of some minerals is a very useful characteristic to use in identifying them. This sulfur for example is almost always yellow.

However, color can be altered by the presence of small amounts of chemical impurities, so…... Color should not be relied on too heavily as an identifying characteristic for most minerals. Agate shows that quartz can occur in many different colors, for example.

Luster Luster is the way in which a mineral reflects, refracts, or absorbs light….in other words the way that it shines. Luster may be “Metallic”...

Or it may be “non-metallic”. Non-metallic mineral lusters include such descriptions as earthy, pearly, glassy, dull, or silky.

Fracture and Cleavage is the way in which a mineral breaks. If the mineral breaks along smooth flat surfaces like calcite or mica, it is said to cleave.

Fracture refers to the characteristic of breaking along rough irregular surfaces. Mineral like quartz are said to “fracture”. Think of a meat cleaver and a bone fracture to keep these terms straight.

Crystal shape The shape of a mineral crystal is determined by the arrangement of its atoms. Each mineral tends to occur in a limited number of crystal shapes.

Streak Streak is the color of the powder left behind when the mineral is rubbed on a piece of unglazed porcelain.

Hardness Hardness is a mineral’s resistance to being scratched. A numerical scale from 1-10 is used to measure hardness. (Moh’s Scale) Talc is the softest mineral at #1. Diamond is hardest (10)

Specific Gravity Specific gravity is the ratio of a mineral’s mass compared to an equal volume of water. In other words, how many times heavier is the mineral than the same amount of water?

Determining Specific Gravity Determine the mass of the mineral Suspend the mineral in a beaker of water and redetermine its mass Find how much mass was lost when the mineral was suspended in water. Divide the mass in air by the amount of mass lost when suspended in water Answer = specific gravity

Common Mineral Groups... Silicates - The 2 most abundant elements in the earth’s crust are oxygen and silicon. These combine to form an atomic structure called a tetrahedron. These tetrahedra form minerals called silicates.

Carbonates A group of minerals in which carbon and oxygen combine to form a carbonate CO3 molecule. The test for these is the bubble test. When exposed to hydrochloric acid they release CO2 and they bubble.