Sedimentary Rock Classification

Sedimentary Rock Classification Schemes

*Clastic Sedimentary Rock Classification*
*Particle Size*	*Sediment Type*	*Rock Name*
COARSE	Gravel
>256 mm (~ 10 in.)	Boulder	*Conglomerate*
256 mm - 64 mm	Cobble
64 mm-2 mm	Pebble
MEDIUM	sand	*Sandstone*
2 mm - 0.062 mm	sand	Quartz sandstone *Arkose* (>25% feldspar)
FINE	mud
0.062 mm - 0.0039 mm	silt	*Siltstone*
< 0.0039 mm	clay	*Mudstone* (if blocky) *Shale* (breaks along bedding planes) *Claystone*

*Biochemical and Chemical Sedimentary Rocks*
*Sediment*	*Chemical Composition*	*Mineral*	*Rock Name*
*BIOCHEMICAL*
Shell Fragments	CaCO3	Calcite	Coquina
Sand & Mud sized	CaCO3	Calcite	Limestone
siliceous grains	SiO2	Quartz, Chalcedony & Opal	Chert and Flint
Peat & organic material	Carbon and Hydrocarbons	Coal, Petroleum	Coal, Oil and Gas
Marine Organisms	CaCO3	Calcite	Chalk
*CHEMICAL*
	Ca-MgCo3	Dolomite	Dolomite or Dolostone
Iron Oxide sediment	Fe2O3 or Fe(CO3)2	Hematite, Limonite, Siderite	Iron Formation
Evaporative Sediments	NaCl, CaSO4	Halite, Gypsum	Evaporite: rock salt or rock gypsum
	Ca3(PO4)	Apatite	Phosporite

Back to the Sedimentary Rocks Lab