SEDIMENTARY ROCKS are derived from pre-existing rocks. The processes of weathering and erosion break rocks down through a variety of mechanical and chemical means. The solid remains of this process as well as the dissolved material can go into making the SEDIMENTARY ROCKS.
Follow the links to the left to see the various kinds of CHEMICAL and CLASTIC (Detrital) sedimentary rocks.
| CLASTIC (DETRITAL) | ||
| COARSE
GRAINED
PEBBLES, COBBLES AND BOULDERS |
CONGLOMERATE |
Rounded fragments with fine grained matrix |
BRECCIA |
Angular fragments with fine grained matrix | |
| MEDIUM
GRAINED
SAND |
QUARTZ SANDSTONE |
Predominantly quartz |
| ARKOSE | Poorly sorted with visible feldspar, commonly reddish brown in color | |
| GRAYWACKE | Poorly sorted with visible mica and or rock fragments, dark gray or greenish gray in color | |
| FINE
GRAINED
SILT AND CLAY |
SILTSTONE | Massive rock composed of gritty equidimensional grains of quartz and feldspar |
SHALE |
Composed of clays that impart a fine layering to the specimen and a tendency to break along those layers | |
| CHEMICAL | ||
| LIMESTONES
CaCO3 All react (fizz) to cold dilute HCl |
CRYSTALLINE | Composed of sugary calcite crystals, usually gray or buff colored |
FOSSILIFEROUS |
Contains fossilized animals or plants in a lime mud matrix | |
| CHALK | Composed of microscopic calcium carbonate remains of plants or animals | |
TRAVERTINE |
Coarsely crystalline deposit typically formed by springs or in caves, often banded and of various colors | |
| OOLITIC | Consists of small carbonate spheres called oolites | |
COQUINA |
Generally made of shells and shell fragments in a beach environment, little or no matrix | |
| EVAPORITES | 
ROCK SALT (NaCl) |
Halite - cubic cleavage and a salty taste |
GYPSUM (CaSO4.H2O) |
Texture varies - it may sugary as in ALABASTER; fibrous as in SATIN SPAR or clear as in SELENITE | |
| OTHERS | DOLOMITE (CaMg(CO3)2 | Generally not fossiliferous, but otherwise similar to limestone; will fizz weakly in HCl when rock is powdered |
| CHERT (SiO2) | Microcrystalline quartz; may be any color (black - flint, red jasper); conchoidal fracture, waxy luster, scratches glass | |
| DIATOMITE | Composed of the microscopic silica shells of plants and animals, soft (breaks easily in hands) and white | |
COAL |
Carbonized remains of plants, black and low density | |