A. Specimens that can be scratched readily with the THUMB NAIL. 1. Become muddy when rubbed with a wet finger. Page Shale 20 Fire Clay 24 Flint Fire Clay 26 Diaspore Clay 27 2. Crumble easily into hard sand grains. Sandstone 30 3. Chalky, white, porous. Tripoli 37 Weathered Chert 36 “Cotton Rock” Dolomite 15 4. Clear and glassy, or glistening white; may split and show glassy, flat faces. Gypsum 63 B. Specimens scratched readily with a POCKET KNIFE, or IRON NAIL but not with the thumb nail. 1. Loose sand grains scratched off. Sandstone 30 2. Granular, but grains are tightly interlocked; also “bubbles” or effervesces in dilute muriatic (hydrochloric) acid. Limestone 10 Dolomite 10 Marble 15 Formed in a cave. Cave Onyx 16 Travertine 16 3. Chalky white, porous. Weathered Chert 36 4. Black. Coal 49 Black Shale 20 5. Pebbles or gravel cemented together. Conglomerate 54 6. Powder becomes muddy when wetted. Hard Shale 20 Flint Fire Clay 26 Diaspore Clay 27 7. 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 8. Yellow, brown, or black and leaves a yellow-to-brown mark or streak when rubbed on a hard white rock or on unglazed porcelain. Limonite 57