Rhyolite Porphyry 45 5. Coarse-grained (BB-shot size to considerably larger), glassy luster where freshly broken; pink, red, grey. Granite 38 Gneiss, like granite but _banded_; occurs in boulders north of the Missouri River 38 6. Coarse-grained, dark green, dark gray, greenish-black. Gabbro 54 Diabase 48 7. Brassy, metallic, heavy; leaves a black to greenish black mark or streak when rubbed on a hard white rock or on unglazed porcelain. Pyrite 51 Marcasite 51 8. Glassy fragments breaking with rough fracture, or may occur in six-sided crystals; clear, water-white, milk-white, gray or pink; in sand grains; in granite. Quartz 41 9. Intense red; leaves a red mark or streak when rubbed on a hard white rock or on unglazed porcelain. Hematite 56 Iron Band Diaspore 58 Paint Ore 58 10. Yellow, brown or black, but leaves a yellow to brown mark or streak when rubbed on a hard white rock or on unglazed porcelain. Limonite 57 ROCK AND MINERAL DESCRIPTIONS Limestone and Dolomite Limestone is a bedded or layered rock found abundantly in Missouri in bluffs, creek beds, hill sides, and is known to underlie the soil in most of the south half of the state. It occurs in thin slabs, thick layers, and in massive beds which may make a small cliff in themselves. Limestone is soft enough to be scratched with steel. It is commonly white to grayish, but may be stained tan, yellowish, or reddish by iron oxide, or darkened through shades of gray to black by the presence of very finely-divided, black carbonaceous matter. It may be microscopically fine-grained (and then it can be used in lithographic printing in the reproduction of very fine images), or its grains may vary in size up to one-half inch in cross section. [Illustration: Limestone (dolomite) bluff near Jefferson City.]