Quartz
Quartz is the most common form of crystalline silica. In fact, it is the second most common surface material accounting for almost 12% by volume of the earth's crust. Quartz is present in many materials in the construction industry, such as brick and mortar, concrete, slate, dimensional stone (granite, sandstone), stone aggregate, tile, and sand used for blasting. Other construction materials that contain crystalline silica are asphalt filler, roofing granules, plastic composites, soils, and to a lesser extent, some wallboard joint compounds, paint, plaster, caulking and putty.
Cristobalite and Tridymite
Cristobalite and tridymite are natural constituents of some volcanic rock. Man-made forms result from conversion of quartz or amorphous silica that has been subjected to high temperature or pressure. Diatomaceous earth, composed of amorphous silica, crystallizes during heating (calcining), yielding a calcined product that contains as much as 75% cristobalite. Cristobalite is also found in the superficial layers of refractory brick that have repeatedly been subjected to contact with molten metal.
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1-2. What is the most common form of silica?
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