Many people examine minerals for recreation, but it's also an invaluable industrial skill.
Hematite, graphite and feldspar have each played a role in human history and industry for literally many thousands of years. Because of their numerous applications in history and daily life, it is very helpful to learn identify these minerals by making elementary observations of their physical traits.
Understanding Mineral Properties
Whether in an academic discussion, an industrial forum or among collectors, minerals are described by a set of physical properties that readily identify them. In general, these properties can be easily ascertained in order to avoid the necessity of a complex chemical analysis. Although there are assessments that may be performed in a laboratory setting, most minerals can be identified by judging a sample's overall sheen (luster), its hardness, how much the mineral tends to cleft into smooth planes (cleavage) and the color of the mineral after it has been pulverized (streak).
Hematite Characteristics
The red color of Mars is the result of hematite on its surface.
Hematite is the primary ore from which iron is derived; hence, it is the origin of most steel products. Its chemical formula is Fe2O3, transcribed as iron (III) oxide. Although hematite samples exhibit a significant variety of colors and textures, all hematite streaks form a rust-red powder. In fact, hematite is chemically identical to rust, and the name "hematite" comes from the Greek word for "blood" on account of its color. Hematite has a metallic luster, and in large pure samples this gives it a silver-like appearance. Hematite's relative hardness is 6.5 (similar to pyrite), and it does not exhibit any cleavage.
Graphite Characteristics
Not to be confused with the metal element, pencil lead is made of graphite.
Graphite is the most common form of pure carbon (the other is diamond) and is most commonly associated with its use as pencil lead. This usage gives graphite its name from the Greek word meaning "to write." Graphite has a sub-metallic luster with a dark appearance that produces a black streak. Because of its chemical purity and elegant molecular symmetry, graphite exhibits perfect cleavage. Unlike diamond, its chemical allotrope, graphite, is a very soft mineral with a relative hardness that typically registers 1.5 to 2, which is only slightly harder than a fingernail.
Feldspar Characteristics
Feldspar is not a single mineral but rather a family of minerals with similar molecular formulas. Feldspar is produced by joining one or more metal atoms to an ion of aluminum silicate. The chemical formulas of plagiocase feldspars have sodium and/or calcium whereas alkali feldspars have potassium. Feldspars, in general, have a dull white color that streaks pure white. Their luster is vitreous, meaning that the surface appears glass-like. Feldspars have a relative hardness between 6 and 6.5, and they exhibit perfect cleavage.
Tags: relative hardness, from Greek, from Greek word, Greek word, pencil lead, perfect cleavage
