Other elements occur only in traces. Table 7.2 reprises some common minerals. The crystal structure is one of the most important clues to identification. One looks at Moh's hardness, streak, luster, and specific gravity. Additional tests like taste, feel, acid effervescence, or magnetic susceptibility are sometimes useful.
Some minerals are fluorescent.
A few rocks form out of one mineral, but most are formed from several. However, these same minerals at the frigid temperatures out here on earth's surface are very fragile, very susceptible to physical and chemical weathering. We classify rocks as Igneous, Sedimentary, and Metamorphic. Igneous rocks can be classified by two attributes. First, by mineral composition.