“Quartz glass: A clear vitreous solid, formed by melting pure quartz, that can withstand high temperatures and is extremely transparent to infrared, visible, and ultraviolet radiations. Also called fused quartz, fused silica.” (from: The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2004, 2000 by Houghton Mifflin Company. Published by Houghton Mifflin Company) Fused quartz is used extensively in scientific lampworking for industry. Take a look at the American Scientific Glassblowing website for more information: www.asgs-glass.org/ Charles Bray gives more information about the different types of quartz: Bray, Charles. Dictionary of Glass: Materials and Techniques, 2nd ed. London: A & C Black; Philadelphia: Univ. of Pennsylvania, 2001, p. 195: “Quartz (SiO2) Silica. this refers to the most common form of mineral silica. Large crystals are quite common, some of which are a milky white, others can be completely clear and transparent. It is a source of white sand when it has disintegrated and this is often ground down to provide batch silica.
Other types of sand are also largely composed of quartz but with traces of other minerals. It is melted in special high temperature furnaces to provide the silica tubing used for so-called infrared heating elements and as supports for elements in kilns. It is a hard mineral and is used as one of the standards on the Mohs’ scale. Powdered quartz is sometimes mixed with plaster of Paris to make moulds for casting or slumping glass. Quartz is the last of the phases of silica resulting from the initial cooling of the Earth. The material starts as molten siliceous material and becomes in turn cristobalite, tridymite and eventually quartz. All the phases have similar chemical composition but differ in their molecular structure. (See silica). Quartz exists in two forms. The alpha form only occurs below temperatures of 573 degrees C (1060 degrees F) whilst the beta form exists only above this temperature. The change can occur in either direction and is known as the silica inversion. The difference lies in the angle of the silica-oxygen-silica bonds. This occurs because the silicon atom is just too large to fit tightly between the oxygen atoms and thus allows some adjustment to take place.
Quartz also provides several crystalline forms used for jewellery such as amethyst, rose quartz, blue quartz, onyx, carpelian and agate. Small prepared quartz crystals are also used to provide accurate timekeeping in both watches and electronic equipment. A quartz crystal will be made to oscillate at a rate of 32768 cycles per second by a very small electrical current.”