Open Adit™ - Mineral Properties / Color

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The color of a mineral is one of its most obvious attributes, and is one of the properties that is always given in any description. Color results from a mineral’s chemical composition, impurities that may be present, and flaws or damage in the internal structure. Unfortunately, even though color is the easiest physical property to determine, it is not the most useful method to characterize a particular mineral. The mineral fluorite (CaF₂) for example, displays a rainbow of colors.

Some minerals do have only a single color that can be diagnostic, as for instance the yellow of sulfur. Also, although many minerals vary in color few span the spectrum of colors as fluorite does. Often we find most color variations of a given mineral are consistently light colored (white, tan, pink, yellow) or dark colored (gray, black, blue, green).

The color of minerals depends on the presence of certain atoms, such as iron or chromium which strongly absorb portions of the light spectrum. The mineral olivine, containing iron, absorbs all colors except green, which it reflects, so we see olivine as green. All natural minerals also contain minute impurities. Some minerals such as corundum get their colors from these these impurities. Blue corundum (sapphire) is formed when small amounts of iron and titanium are dissolved in the solid crystal. Finally some crystals get their color from growth imperfections. Smoky quartz (black) is a good example. Growth imperfections interfere with light passing through the crystal making it appear darker, or almost black.

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