New York State High School Regents Exam Prep|
What are minerals?
Minerals are naturally occuring, inorganic, uniform materials that have definite chemical and physical properties.
Color- The most easily observed property, but usually the least useful. A mineral's color can be changed by the impurities that are found in the mineral.
Luster- The way light is reflected from a newly exposed surface. Described as either metallic or nonmetallic. Some examples of minerals with metallic luster are pyrite, galena and magnetite. Some examples of minerals with nonmetallic luster are calcite, quartz and feldspar. Nonmetallic luster can also be described as glassy, pearly, waxy and earthy (dull).
Streak- The color of the mineral in powder form. This test is done by rubbing the mineral across a white streak plate. Several minerals have a streak that is not the same color as the mineral itself. Most metallic luster minerals have a dark colored streak.
Crystal Structure- Some minerals form crystals, if there is time and room for the crystals to form. The crystal pattern of a mineral is controled by the internal arrangement of the atoms that make up the mineral. Some examples of these crystal structures are quartz which has a hexagonal (six-sided) crystal and halite which has a cubic crystal.
Hardness- The ability of one mineral to scratch another. The softer mineral gets scratched. You test a mineral's hardness by scratching the unknown mineral with an object of known hardness. Moh's Scale of Hardness is used to rate the hardness of a mineral. The chart below shows the ten minerals that make up the hardness scale and some common materials with their hardness to test unknown minerals. One on the scale is the softest and ten is the hardest.
To find the hardness of a mineral you first have to find out what it can scratch and what can scratch it. For example, if a mineral can scratch glass but can't scratch a streak plate, the mineral has a hardness of 6 on the Moh's Hardness Scale.
New York State High School Regents Exam Prep Center: Earth Science