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Quartzite (225 words) |
 | Pure quartzites are a source of silica for metallurgical purposes and for the manufacture of brick. |
| In microscopic section the clastic structure of some quartzites is well preserved; the rounded sand grains are seen with quartz overgrowths deposited in crystalline continuity, so that optical properties of the grains are similar to those of the material surrounding them. |
| Many quartzites, however, have been crushed, and the quartz largely is a mosaic of small, irregularly shaped crystalline fragments with interlocking margins. |
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