QUARTZ

Quartz has always played a large role in human technology. Critical items from some of man’s earliest stone tools to latest electronic components were made of quartz. Native peoples of Indiana used quartz for many vital tasks. Today quartz is used in many products as a raw material for huge amounts of construction materials, such as glass, concrete, or mortar, and quartz is refined to yield silicon which is critical for computers and other high technology mainstay of modern life (Fig. 2). Quartz is still used for many modern Industrial materials (Fig. 3).

Quartz is made when atoms of silicon and oxygen bind in the form of a tetrahedron. The nature of the atoms and the resulting crystal structure (Fig. 4) lead to its extraordinary durability. Quartz has a scratch hardness of 7 and often forms hard, tough fragments that withstand all sorts of mechanical and chemical attacks. Crystals form clear hexagonal (6-sided) forms when space allows (Fig. 1).

Quartz is a major component of many types of rock. Quartz is abundant in certain igneous rocks. It forms the clear to grey or even white lumpy blobs in granite and comprise most of silicate-rich or felsic igneous rocks. It is absent or rare in more primitive basic or silica-poor igneous rocks such as basalt. Quartz is almost never present in meteorites.

Metamorphic rocks contain abundant quartz especially those produced from granites, sandstones, or shales. In particular, coarser-grained metamorphic gneiss is marked by distinct bands of quartz and other minerals. Sandstones are almost pure quartz.

Sedimentary rocks (those formed by physical or chemical accumulation of preexisting fragments of minerals or sediments) plus a few rocks formed by chemical precipitation are the most common in Indiana provide the largest quantity and greatest variability of quartz form.

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