Granite at the “Elephant Rocks,” Graniteville. The large boulders now rounded by weathering are remnants of a higher part of the large granite body which underlies this region. (Photograph courtesy of Mr. Noel Hubbard).
Granite is an intrusive igneous rock; that is, it solidified from a hot liquid state (like lava) in a large body, beneath, or surrounded by pre-existing rocks. Because of slow solidification a coarse-grained texture was developed. In southeastern Missouri where granite is now exposed at the surface (for example, the Elephant Rocks State Park at Graniteville), that granite was covered originally by hundreds of feet of rock at the time it solidified from a liquid. During the millions of years which have elapsed since the granite solidified, its cover and the upper part of the granite have been eroded away by streams and rain after weathering to soil material. In fact, the ocean has covered the area several times during its long geological history.
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 of Ironton | Granite 6 miles east 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.
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.
Quartz occurs in granite as the lustrous, partially rounded grains which constitute perhaps 20% of the rock (feldspar makes up most of the more opaque remainder which breaks with many small flat faces), and is recognized in the small glistening grains in the porphyry. Hence it is an important igneous rock-forming mineral.