Weathering, Soil, and Sedimentary Rocks - The Changing Earth: Exploring Geology and Evolution - page 151

Sediment Process Rock

Gravel > 2 mm Compaction/cementation

Conglomerate

Rounded clasts

Sedimentary
breccia

Angular clasts

Sand 2 mm- 16 mm Compaction/cementation

Quartz sandstone
(mostly quartz)

Sandstone

Arkose
(> 25% feldspars) 1 1

Silt 16 mm - 256 mm Compaction/cementation

Siltstone Mostly silt

1

Mudstone Silt and clay

Clay < 256 mm Compaction

Shale if
fissile*

Claystone Mostly clay

*Fissile refers to rocks capable of splitting along closely spaced planes.

◗ Figure 6.18 Lithifi cation and Classifi cation of Detrital Sedimentary Rocks Notice that little
compaction takes place in gravel and sand.

TABLE 6.2 Classifi cation of Chemical and Biochemical Sedimentary Rocks

Chemical Sedimentary Rocks

Texture Composition Rock Name

Varies Calcite (CaCO 3 ) Limestone

Carbonate rocks

Varies Dolomite [CaMg(CO 3 ) 2 ] Dolostone

Crystalline Gypsum (CaSO 4 ·2H 2 O) Rock gypsum

Evaporites

Crystalline Halite (NaCl) Rock salt

Biochemical Sedimentary Rocks

Clastic Calcite (CaCO 3 ) shells Limestone (various types, such as chalk and coquina)

Usually crystalline Altered microscopic shells of SiO 2 Chert (various color varieties)

Carbon from altered land plants Coal (lignite, bituminous, anthracite)

gravel has experienced little transport, probably less than
a kilometer. Considerable energy is needed to transport
gravel, so conglomerate is usually found in environments
such as stream channels and beaches.
Sand is a size designation for particles between 1/16
and 2 mm, so any mineral or rock fragment can be in
sandstone. Geologists recognize varieties of sandstone
based on mineral content (Figure 6.18). Quartz sandstone

is the most common and, as the name implies, is made up
mostly of quartz sand. Another variety of sandstone called
arkose contains at least 25% feldspar minerals. Sandstone
is found in many depositional environments, including
stream channels, sand dunes, beaches, barrier islands,
deltas, and the continental shelf.
Mudrock is a general term that encompasses all detrital
sedimentary rocks composed of silt- and clay-sized particles