Common Minerals
LIGHT-COLORED MINERALS Light-colored minerals are generally lacking in the elements iron (Fe) and magnesium (Mg). Some of the most common light-colored minerals are listed below in order of decreasing hardness.	DARK-COLORED MINERALS Dark-colored minerals (black, brown, dark green, gray) are generally rich in iron (Fe) and/or magnesium (Mg). Some of the most common dark-colored minerals are listed below in order of decreasing hardness.
QUARTZ FELDSPAR CALCITE HALITE MUSCOVITE GYPSUM	OLIVINE MAGNETITE AUGITE HORNBLENDE HEMATITE BIOTITE

MINERALS: A mineral is a naturally occurring inorganic solid element or compound with a particular chemical composition (small variations are allowed) and a characteristic internal arrangement of its atoms. In the field, minerals are generally identified by their physical properties: hardness, cleavage, density, color, and reaction to dilute hydrochloric acid (HCl). The hardness of a mineral is an indication of its "scratchability" - a mineral can scratch other objects of equal or lesser hardness. Hardness is usually measured on a 1-10 scale (the Moh's scale), with 10 (diamond) being the hardest known mineral. It will usually be enough to determine an approximate hardness for a mineral by testing it against a glass plate (H=5.5) and against your fingernail (H=2.5). Cleavage is the tendency of some minerals to break along certain planes of weakness in their atomic structures. A set of such parallel planes of weakness constitutes a cleavage direction. Minerals may have several different cleavage directions oriented in a variety of ways to one another. Look for flat, reflective surfaces on the mineral sample - a set of parallel surfaces would be a good indication of cleavage. The density of a mineral is a measure of how heavy it is for its size. Minerals containing large amounts of heavy elements (lead, iron, etc.), or with tightly packed atoms, tend to have higher densities than other minerals. The colors of mineral samples are often quite variable - being determined by the presence or absence of impurities. The color of the mineral when powdered (its streak) is sometimes more characteristic than the apparent color. Only one mineral, magnetite, is strongly magnetic - though hematite (another iron mineral may be slightly magnetic). Only one mineral, calcite, reacts vigorously with dilute hydrochloric acid.