Explanation of lithologic terms

claystone: all fine-grained siliciclastic rocks consisting entirely of clay, whether lithified or not. Includes clay, claystone. Also see siltstone, mudstone and "shale".

mudstone: fine-grained siliciclastic rocks containing between silt and clay sized particles, but not less than 33% of either. May be lithified or not. Includes mud, mudstone. Also see siltstone, claystone and "shale".

"shale": fine-grained siliciclastic rocks containing unknown proportions of clay and silt, but containing at least 33% clay. May be lithified or not. Avoid using this category, except in cases where the proportions of clay and silt are not known. This will be a catch-all category for poorly described fine-grained siliciclastic rocks. Also see: claystone, mudstone, siltstone.

siltstone: fine-grained siliciclastic rocks containing less than 33% clay and more than 67% silt size particles. May be lithified or not. Also see claystone, mudstone and "shale".

sandstone: siliciclastic rocks composed dominantly of grains less than 2 mm in diameter and greater than 65 (roughly the limit of what is visible with a 10x hand lens)

conglomerate: siliciclastic rocks dominantly composed of grains greater than 2 mm. Carbonate rocks composed of grains greater than 2 mm should be named using one of the carbonate names below.

marl: a rock consisting of 35% to 65% clay and 35% to 65% lime mud.

lime mudstone: a limestone composed almost entirely of lime mud (micrite) and less than 10% grains (ooids, peloids, bioclasts, or intraclasts). Note that a lime mudstone is a carbonate rock. A rock composed of siliciclastic mud but with carbonate cement should be treated as one of the fine-grained siliciclastic rocks ("shale", claystone, mudstone, siltstone).

wackestone: a limestone composed of lime mud (micrite) and greater than 10% grains (ooids, peloids, bioclasts, or intraclasts). Wackestones are matrix-supported, that is, grains do not support one another with lime mud simply filling in between grains.

packstone: a limestone composed of grains (ooids, peloids, bioclasts, or intraclasts) and lime mud (micrite). Rock is grain-supported and micrite simply fills in spaces between grains that are in contact with one another.

grainstone: a limestone composed of grains, but lacking lime mud (micrite). Spaces between grains are filled with spar (cement).

"reef rocks": carbonate rocks in which growing organisms trapped and bound sediment between them. Includes bafflestone, boundstone, etc.

"limestone": category to use when a limestone cannot be classified into one of the preceding lithologies. Avoid using if possible. Chalks should be placed into this category.

dolomite: category to use for all carbonate rocks composed primarily of dolomite.

"carbonate": category to use for a carbonate rock that cannot be classified as either a limestone or a dolomite. Avoid using if possible.

chert: a rock composed of cryptocrystalline silica. May form beds or nodules. If chert is not the dominant material in the rock, but is instead an accessory to another rock type, say a grainstone, then the rock should be called a grainstone, and siliceous should be selected as an adjective.

phosphorite: a rock composed dominantly of grains of phosphate, which may be in the form of ooids, peloids, or other forms. If phosphate is not the dominant material in the rock, but is instead an accessory to another rock type, say a grainstone, then the rock should be called a grainstone, and phosphatic should be selected as an adjective.

ironstone: a rock composed dominantly of hematite, chamosite, goethite, etc. If iron minerals are not the dominant material in the rock, but are instead an accessory to another rock type, say a grainstone, then the rock should be called a grainstone, and ferruginous should be selected as an adjective.


Translations of lithologic terms

arenite: sandstone

arkosic arenite: sandstone

arkosic wacke: sandstone; adjective: argillaceous

bafflestone: "reef rocks"

biomicrite: wackestone; adjective: shelly/skeletal

biomicrudite: wackestone; adjective: shelly/skeletal

biosparite: grainstone; adjective: shelly/skeletal

boundstone: "reef rocks"

buff: yellow

calcarenite: grainstone

calcilutite: lime mudstone

calcirudite: "limestone"

calcisiltite: grainstone

carbonate: "carbonate"

chalk: "limestone"

chert: chert

clay: claystone; lithification: unlithified

claystone: claystone

conglomerate: conglomerate

dolomite: dolomite

flat-pebble conglomerate: grainstone or packstone; adjective: flat-pebble

floatstone: "reef rocks"

grainstone: grainstone

graywacke: sandstone; adjective: argillaceous

indurated: lithified

intramicrite: wackestone; adjective: intraclastic

intramicrudite: "limestone"; adjective: flat-pebble

intrasparite: grainstone; adjective: intraclastic

ironstone: ironstone

lime mudstone: lime mudstone

limestone: "limestone"

lithic arenite: sandstone

lithic wacke: sandstone; adjective: argillaceous

lithographic limestone: lime mudstone

marl: marl

micrite: lime mudstone

oomicrite: wackestone; adjective: ooidal

oosparite: grainstone; adjective: ooidal

packstone: packstone

pelmicrite: wackestone; adjective: peloidal

pelsparite: grainstone; adjective: peloidal

phosphorite: phosphorite

quartz arenite: sandstone

quartz wacke: sandstone; adjective: argillaceous

rudstone: "limestone"

sand: sandstone; lithification: unlithified

sandstone: sandstone

shale: "shale"

silt: siltstone; lithification: unlithified

siltstone: siltstone

wacke: sandstone

wackestone: wackestone


Can't find your term? We may need to add it to the list. Contact Steven Holland at stratum@uga.edu.