Geologists use many methods to classify minerals and determine their identities. Types of classification include hardness, streak, color, luster, cleavage, tenacity, magnetism, and many more. These methods listed are generally the easiest to use without extra materials or an advanced education in geology. Most of these methods seem self explanatory but are actually more complex and involved than most would expect, except color and magnetism which are obvious in their meaning.
Streak helps determine the true color of a mineral because a mineral’s powder is sometimes a different color than the color a mineral appears and this helps identify the mineral’s true composition. For example hematite is a shiny grey color but its streak is brown. To test streak the mineral sample is rubbed against an unglazed piece of ceramic.
Luster describes the appearance of the mineral overall. A mineral can have a metallic luster or a nonmetallic luster. If the luster is nonmetallic it is then said to be glassy, greasy, pearly, silky, or dull/earthy. This is done by just looking at the mineral and using one’s own judgment. Cleavage is defined as the tendency of a mineral to break along definite planes of weakness that exist in the mineral’s atomic structure. There are many types of cleavage but when doing basic classification it is only important to know whether or not a mineral has a definite plane of cleavage.
Tenacity is the mineral’s ability to resist being broken or bent. Types include brittle, sectile, malleable, flexible, and elastic. Hardness of a mineral is a measure of its resistance to scratching. Different materials represent different degrees of hardness like being scratched by a penny gives that mineral a hardness of 3.5 or being scratched by steel nail gives a mineral a hardness of 5-6. Hardness like color and luster is generally easy to test because the objects needed can be found easily. Overall these methods are not full proof but they do help narrow down the possible identities of a mineral which is useful in the field when a researcher might just need to know the general group a specific mineral might be found in.
A specific mineral that can be found locally and is known for its hardness is Kyanite. Kyanite can be found at nearby Crowder’s Mountain State Park. It is a metamorphic mineral composed of aluminum, silica, and oxygen that generally forms from clay-rich sedimentary materials being exposed to high pressure. Its color varies greatly but it always has a white streak. Its luster is pearly and it has cleavage. Its hardness is unique not only because of its high strength but because it has two. The hardness on one side of the crystal is 5 and the hardness on the part of the crystal perpendicular to this spot is 7. Due to the fact that Kyanite retains its strength at high temperatures it is used for many things such as the inside of kilns, automotive and train parts, and porcelain. Kyanite has some unique properties such as its expansion at high temperatures. It is a very useful mineral and its usage should be monitored so that this resource does not become depleted.