Minerals Among Us
Venture outside on any particular day, look down along the traversed path and select a rock, any rock, call it Exhibit A. Observe it for a moment. How fantastic would it be, to positively identify it? To know that by observing certain properties of this rock, it can be said with confidence, that this particular rock has calcite, halite, mica, quartz or any specific mineral. Well, “because the atomic structure of a mineral species is always the same, most of its physical properties are relatively constant and may be used for the mineral’s identification” (Gardiner and Wilcox 107).
There are many intriguing physical properties to mineral identification. Visible properties include color, luster, streak, crystal form, cleavage. The tactile property can be measured using Mohs scale, which measures hardness of minerals compared to common objects. Additional tests can be used; including acid, magnetism, smell, taste, and specific gravity.
Taking Exhibit A, the most obvious physical property would be to observe its color. It is the least reliable and often misleading property, due to impurities or exposure to the elements. A mineral such as quartz may be colorless, or have various colors. By observing the color, it can be determined if the mineral is mafic or felsic; dark or light. Luster is observing the sample for metallic or non-metallic properties. If metallic, it will reflect light, like gold; if non-metallic, it can be glassy, pearly or dull. If Exhibit A is used to draw a line over a pavement, the mineral powder left behind would be referred to as the streak. This can be the color of the rock itself or different. Streak is very important in telling true minerals from fake. For example, gold has a yellow streak, whereas “fool’s gold (pyrite)” has a greenish-black streak (Gardiner and Wilcox 110). Crystal form and cleavage can be viewed using a magnifying glass or sometimes with the naked eye. By observing the sample for...
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