ROCK IDENTIFICATION KEY
SAMPLE Scratch with a knife and apply dilute acid (HCl) If rock does not scratch, go directly to I, II, or III
No effervescence or very slight effervescence I Coarse-grained ([p. 37]) II Fine-grained ([p. 38]) III Organic ([p. 39]) Slight effervescence gray, light gray, white, or brown: Dolomite Vigorous effervescence Composed of pebbles that effervesce Rounded pebbles: Limestone conglomerate Angular pebbles: Limestone breccia Composed of crystals of calcite, fossil shells, or oolites: Limestone Composed of banded layers of crystalline calcite; commonly found in caves, forming stalactites and stalagmites: Travertine Large amount of insoluble residue left on acid-treated surface Individual grains seen with unaided eye: Calcareous sandstone Individual grains not seen with unaided eye: Calcareous shale Composed of porous or cellular mass of calcite; commonly found near springs and waterfalls: Tufa