| 31. | The Greathouse Visitor Center is named after R . Marvin Greathouse, who was a pioneer silica sand miner.
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| 32. | Silica sand fills the third layer which gives added grip to cleats as they dig into the surface.
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| 33. | One empty aquatic snail shell should be provided for each individual, along with a thin layer of silica sand.
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| 34. | The park is built around a complex network of mining tunnels, once used to mine coal and silica sand.
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| 35. | Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concrete.
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| 36. | However, there are also a number of smaller producers, chiefly industrial carbonates, silica sand and fluorspar, with a single site.
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| 37. | It was built by Pittsburgh Plate Glass, which was attracted by the area's silica sand, vital to the glass-making process.
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| 38. | Further west is a large field of shale oil, then sedimentary and basalt rocks supplying silica sand, and then coal.
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| 39. | Those blades are planted in artificial dirt, made up of ground-up crumbs of old tires, tennis shoes and silica sand.
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| 40. | In the 1970s there was a proposal to establish a silica sand mine on the north shore of the Endeavour.
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