C

L

A

S

T

I

C

Grain Size

Composition

Shape/Description

ROCK NAME

Gravel size >2mm

Fragments or any rock type - quartz, quartzite, and chert dominant

Rounded

Conglomerate

Angular

Breccia

Sand size 2mm - 0.0625 mm

Mostly quartz

Relatively uniform grain size

Quartz Sandstone

Mostly feldspar

Pink K-Feldspar present

Arkosic Sandstone

Silt size 00039 to 0.0625 mm

Quartz grains, feldspar grains, clay minerals

Siltstone

Clay size <0.0039 mm

Clay minerals

Fissile

Shale

Clay minerals

Non-fissile

Claystone

B

I

O

G

E

N

I

C

Mostly calcium carbonate (CaCO₃)

Fizzes with cold dilute HCl

Muddy matrix with fossils

Fossiliferous Limestone (Wackstone)

>2mm

Shells or shell fragments poorly cemented to form porous, earthy rock)

Coquina

<0.0625 mm

Chalk

<0.0039 mm

Shells or shell fragments well cemented to form dense rock

Micrite (Calcareous Mudstone)

Dull brown and plant-like

Porous and easy to break apart in plant fragments

Peat

Woody appearance, light weight

Lignite

Highly altered plant remains (Carbon)

Black, dense and brittle or porous and sooty

Bituminous Coal

E

V

A

P

O

R

I

T

E

<2mm

Mostly calcium carbonate (CaCO₃)

Fizzes with cold dilute HCl

Spherical grains like tiny beads with concentric laminations

Oolitic Limestone

Coarse crystalline

Banded

Travertine

Cryptocrystalline

Variety of Quartz (SiO₂)

Scratches glass

Chert

Fine to coarse crystalline

Gypsum (CaSO₄·2H₂O)

Can be scratched with fingernail

Rock Gypsum

Fine to coarse crystalline

Halite (NaCl)

Salty taste

Rock Salt