Sedimentary Rock Classification Table

Laboratory 4

Sedimentary Rock
Classification Table

Pamela J. W. Gore

Department of Geology, Georgia Perimeter College

Clarkston, GA 30021

Use this table to help you to identify the sedimentary rocks.

Grains visible	Clasts or allochems larger than 2 mm	Grains are all shell fragments; no mud; fizzes in acid	Coquina
		Clasts and matrix fine grained; clasts are limestone and may be flat and laminated; fizzes in acid	Intraclastic limestone
		Matrix color variable; multiple clast lithologies; clasts differ from matrix in color or composition	Breccia (angular clasts)
			Conglomerate (rounded clasts)
	Clasts or allochems smaller than 2 mm	White or colorless grains, mostly quartz	Quartz sandstone
		Contains pink, gray, or white feldspar (look for cleavage); feldspar grains may be weathered to white kaolinite	Arkose
		Contains rock fragment grains, mostly dark green or gray grains (such as basalt or shale fragments)	Litharenite or lithic sandstone or graywacke
		Round grains with concentric laminations; fizzes in acid	Oolitic limestone
		Dark red to brown, red-brown streak, may contain replaced oolites or fossils, may fizz in acid; may be dense and heavy	Oolitic hematite or oolitic ironstone or fossiliferous ironstone
Grains not visible	Fizzes in HCl acid	White, soft, and powdery	Chalk
		Gray, black, brown or tan; compact, dense. Very fine grained (clay-sized)	Micrite or calcilutite
		Fossils in lime mud matrix	Fossiliferous limestone
		Coarse crystalline mosaic, brown and white color bands, may be cylindrical (stalactite)	Travertine
		Fine to coarse crystalline mosaic; compact, dense, massive	Crystalline limestone
	Fizzes in acid when scratched and powdered	Gray or black, weathers yellowish gray to brown; compact, dense, massive; dolomite	Dolostone
	Does not fizz in acid	Fissile (breaks into thin layers); may be softer than fingernail; clay-sized texture; commonly gray, black, brown or red	Shale
		Feels gritty to the fingernails; commonly gray, black, brown, or red	Siltstone
		Salty taste, may feel slippery; often clear and transparent; cleavage	Rock salt
		Softer than fingernail; white, pink, clear; may be fibrous, fine-grained, or crystalline	Rock gypsum
		Hard - scratches glass; opaque; color variable; smooth feel; may have conchoidal fracture	Chert
		White; looks like chalk but does not fizz in acid; very low density (may float); porous	Diatomite
		White; looks like chalk but does not fizz in acid; dense (does not float); may stick to moistened finger	Kaolinite
		Black, bright and shiny (may almost look metallic in luster), compact, low density	Anthracite Coal
		Black, may leave sooty marks on fingers or paper, may have layers	Bituminous Coal
		Brown to black, crumbly, very soft; porous	Lignite
		Brown, porous, soft; resembles peat moss	Peat

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This page created by Pamela J. W. Gore, pgore@gpc.edu
Georgia Perimeter College

June 30, 1998
Modified December 21, 1998
Updated Decemer 2, 2003