Grain size

Classification of sediments based on grain size composition (Folk, 1954, modified).

Grain size	Abbr.	Definition/description	Code
Clay	Cl	Clay:silt ratio >2:1 and clay+silt >90%, sand <10%, gravel <2%	10
Organic mud	-	Clay:silt ratio from 1:2 to 2:1 and clay+silt >90%, sand <10%, gravel <2%. High content of organic material.	15
Mud	M	Clay:silt ratio from 1:2 to 2:1 and clay+silt >90%, sand <10%, gravel <2%	20
Mud with sediment blocks	-	Mud alternating with blocks of hard sediments	21
Sandy clay	sCl	Clay:silt ratio >2:1 and clay+silt >50%, sand <50%, gravel <2%	30
Sandy mud	sM	Clay:silt ratio from 1:2 to 2:1 and clay+silt >50%, sand <50%, gravel <2%	40
Silt	Z	Clay:silt ratio <1:2 and clay+silt >90%, sand <10%, gravel <2%	50
Sandy silt	sZ	Silt:clay >2:1 and clay+silt >50%, sand <50%, gravel <2%	60
Clayey sand	clS	Sand >50%, clay:silt ratio >2:1 and clay+silt <50%, gravel <2%	70
Muddy sand	mS	Sand >50%, clay:silt ratio from 1:2 to 2:1 and clay+silt <50%, gravel <2%	80
Silty sand	zS	Sand >50%, silt:clay ratio >2:1 and clay+silt <50%, gravel <2%	90
Fine sand	-	Sand >90%, includes fine and very fine sand (Wentworth, 1922)	95
Sand	S	Sand >90%, clay+silt <10%, gravel <2%	100
Coarse sand	-	Sand >90%, includes medium, coarse and very coarse sand (Wentworth, 1922)	105
Gravelly mud	gM	Sand:silt+clay ratio <1:9, gravel 2-30%	110
Gravelly sandy mud	gsM	Sand:silt+clay ratio from 1:9 to 1:1, gravel 2-30%	115
Gravelly muddy sand	gmS	Sand:silt+clay ratio from 1:1 to 9:1, gravel 2-30%	120
Gravelly sand	gS	Sand:silt+clay ratio >9:1, gravel 2-30%	130
Muddy gravel	mG	Gravel 30-80%, sand:silt+clay ratio <1:1	140
Muddy sandy gravel	msG	Gravel 30-80%, sand:silt+clay ratio from 1:1 to 9:1	150
Sandy gravel	sG	Gravel 30-80%, sand:silt+clay ratio >9:1	160
Gravel	G	Gravel >80%	170
Gravel and cobbles	GC	Dominant grain sizes are gravel and cobbles.	174
Gravel, cobbles and boulders	GCB	Dominant grain sizes are gravel, cobbles and boulders.	175
Cobbles and boulders	CB	Dominant grain sizes are cobbles and boulders.	180
Sand, gravel and cobbles	SGC	Dominant grain sizes are sand, gravel and cobbles.	185
Sand and boulders	SB	Bimodal bottom type with frequent instances of blocks on the sandy bottom.	190
Mud/sand with cobbles/boulders	S/M-C/B	Bimodal bottom type where cobbles and boulders occure frequently in the areas dominated by fine-gained sediments.	205
Mud, sand, gravel, cobbles and boulders	MSGCB	Poorly sorted sediments comprising mud, sand, gravel, cobbles and boulders in varying composition with a minimum of 20% mud in the matrix.	206
Cobbles/boulders covered by slam/sand	C/B-S/M	Very coarse sediments covered by fine material.	210
Sand, gravel, cobbles and boulders	SGCB	Poorly sorted sediments comprising sand, gravel, cobbles and boulders in varying composition with a maximum of 20% mud in the matrix.	215
Compacted sediments or sedimentary bedrock	-	Submarine outcrop of compacted sediments or sedimentary bedrock.	300
Bioclastic material (corals, coral reef)	-	Sediments of various grain size (mud, sand and gravel to whole coral reef) created by corals.	500
Thin or discontinuous sediment cover on bedrock. Sediments with varying grain size.	-	Lateral variation of small basins with sediments and exposed bedrock, and/or bedrock with thin/discontinuous sediment cover. Sediments in small basins may have varying grain size.	1
Exposed bedrock	-	Areas without sediment cover.	5
Unspecified	-	Grain size is not specified.	0