- Structure of the Geosphere.
- Earth's crust: types and composition.
- Minerals: concept, occurrence and properties.
- Rocks: rock cycle, main types and uses.
Sedimentary rocks can be made up of clasts or detritus (rock grains) weathered from other rocks by river waters, wind, coastal sea waters, glaciers, living beings, etc. This kind of sedimentary rocks are called detrital rocks.
They're classified upon the grains that they are made up of. First up, grains may be all the same size, uniform, as in a sandstone, or different sizes, as in a conglomerate. Secondly, grains may be bigger or smaller. The following table shows roughly how rock grains are classified upon their size:
|Clay||< 0.004 mm|
|Silt||< 0.06 mm|
|Sand||< 2 mm|
|Gravel||< 6 cm|
|Cobble||< 25 cm|
|Boulders||> 25 cm|
The term lustre refers to the appearance of a mineral surface in reflected light. The main types of mineral lustre are the following:
|Vitreous||Translucent||Quartz, Halite, Olivine|
|Resinous||Translucent||Yellow and red sphalerite varieties|
|Pearly||Poorly translucent||Orthoclase, Mica aggregates|
|Dull metallic||Opaque||Cinnabar aggregates|
|Metallic||Opaque||Pyrite, Chalcopyrite, Magnetite|