Silicon Dioxide, SiO2

Quartz is by far the most abundant of the polymorphic forms of silica and the most widespread and abundant mineral of the earth's crust. It occurs in igneous, metamorphic and sedimentary rocks as well as hydrothermal veins, metasomatic and hot spring deposits.

Amethyst is one of the many varieties of "gemmy" quartz of interest to rockhounds. Others are rock crystal, smoky quartz, citrine, quartz cat's-eye, tiger-eye, rose quartz, aventurine, chalcedony, agate, carnelian, sard, bloodstone, jasper, plasma, and chrysoprase.

Rough amethysts are found as crystals lining druses in various igneous rocks such as granites and gneiss. Amethysts vary in color from faint violet to a deep purple, the darker specimens generally being considered the most desirable. Included manganese dioxide is probably responsible for the deep purple colorations although there may be other tinctural mechanisms involved. Most amethysts fade when subjected to exposure by strong sunlight, and the color may be restored by exposure to beta and gamma rays.

Rocks from WSU Thomas Edison Mineral Collection

Index of Specimen Images

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