Sand b) Solid rock consisting largely of quartz; can be separated easily into individual particles; granular; breaks around rather than through grains Sandstone (8) II FINE-GRAINED ROCKS A. Cannot be scratched easily with a knife; crystals or particles not easily seen with the unaided eye; very hard, difficult to break; may contain a few crystals or particles large enough to see; granular 1) Dense; brittle; splintery or conchoidal fracture; sharp edges and corners when broken; often associated with limestone; usually white or gray; very dense, dull varieties called flint Chert (27) 2) Light gray, pink, red, or tan varieties common; boulders or fragments in the glacial drift Felsite 3) Dark gray, greenish, black, or maroon varieties common; may have small mineral-filled cavities; occurs as boulders or fragments in the glacial drift Basalt (4) 4) Essentially quartz; grains may be identifiable; specimens break through rather than around grains Quartzite (9) B. May or may not be scratched with a knife; fairly uniformly fine grained 1) Soft; feels slippery or soapy when wet; may disintegrate in water; gives off an earthy odor when breathed upon Clay 2) Loose; gritty; particles smaller than table salt Silt 3) Solid rock; often in thin beds or sheets; separates into silt; mica flakes may be present; may contain fossils; may effervesce slightly Siltstone 4) Solid rock; breaks into thin platy sheets; may feel slippery when wet; black to gray; may contain fossils; shows thin laminations; may effervesce Shale (10) 5) Solid rock: does not break into thin platy fragments; may effervesce slightly Mudstone 6) Solid rock; usually gray or black; splits into platy sheets or slabs; harder than shale Slate 7) Powdery; white or light brown; commonly associated with chert and quartz from which it forms Tripoli (19) III ORGANIC ROCKS (DARK COLORED)