Hardness: 7.0 Specific Gravity: 2.65
Characteristics: Variety of quartz, purple colored due to iron impurities and radioactive decay; vitreous luster; conchoidal fracture; only soluble in HF.
A common mineral found in igneous rocks, many metamorphic rocks, and most sedimentary rocks.
As a crystal or in cryptocrystalline form, amethyst is used as a decorative stone in collections and jewelry. Quartz has many other uses such as in pressure gauges, oscillators, resonators, and wave stabilizers. Due to the mineral's optical characteristics it is used in heat-ray lamps, prisms, and spectrographic lenses. Also used in the manufacture of glass, paints, and abrasives.
(Primary text: Perkins, D. 2002. Mineralogy. Prentice Hall.)