Missouri has a fine quality of granite in large quantity in southeastern Missouri. Granite is used for building, structural and monument purposes (see discussion under marble), for rubble stone, rip-rap, ballast, gravel, paving blocks, crushed chicken gravel, and for other specialized uses where favorably located. Chemical analyses of granite and porphry, taken from Missouri Geological Survey Report, Volume VIII, 1895, follow. Porphyry 6 miles east Granite 6 miles east of Ironton of Ironton SiO₂ 71.88 72.35 Al₂O₃ 12.88 13.78 Fe₂O₃ 3.05 1.87 FeO 1.05 0.36 CaO 1.13 0.87 MgO 0.33 0.42 K₂O 4.46 4.49 Na₂O 4.21 4.14 P₂O₅ 0.15 0.13 TiO₃ 0.22 0.44 Ignition loss 0.26 0.54 The glacial granite boulders found in central to northern Missouri also solidified as intrusive rock in the northern United States or in Canada. After being exposed at the surface they were picked up and carried down by the geologically recent, continental ice sheet (glacier) that moved down from Canada to across the northern half of Missouri. Scratches and grooves may have been cut in some of these boulders, or flat faces scoured and planed off as they were scraped against other hard rocks. Quartz gravel is usually present, often in abundance, in glacial deposits. Small specimens of native metallic copper, which come from near Lake Superior, have been found in Missouri glacial deposits. Even diamonds from an unknown source in the north were carried by the ice down into the United States. The history of the glaciation is a spectacular account of changes which our continent has undergone in the geological past. [Illustration: Glacial scratches on boulder carried by the large glacier in northern Missouri long ago. Boulder from near Columbia.] Quartz Quartz is a mineral of wide-spread occurrence which is characterized by the following properties: (1) it is considerably harder than glass or steel, (2) it has a high luster, glassy to oily, (3) it breaks with an irregular or rough glistening fracture, and (4) it crystallizes in six-sided crystals when it grows unobstructed. Ordinary acids do not attack quartz, and it is relatively unaffected by chemical weathering in Missouri. Its composition is silicon dioxide, SiO₂.