Microscopic:
* Clay minerals: < 0.004 mm (4 microns)
* Silt: 0.004 mm - 0.063 mm
* Fine sand: 0.063 mm - 0.2 mm
* Medium sand: 0.2 mm - 0.63 mm
* Coarse sand: 0.63 mm - 2 mm
Macroscopic:
* Very coarse sand: 2 mm - 4 mm
* Pebbles: 4 mm - 64 mm
* Cobbles: 64 mm - 256 mm
* Boulders: > 256 mm
Factors influencing grain size:
* Source rock: The original rock from which the sediments were derived influences the initial grain size.
* Weathering and erosion: These processes break down rocks into smaller particles, reducing grain size.
* Transportation: The distance and method of transportation (water, wind, ice) can further affect grain size.
* Depositional environment: The environment in which sediments are deposited (e.g., lake, river, ocean) also influences grain size.
Note: These size ranges are general guidelines, and there is overlap between categories.
Beyond size, other characteristics are also used to describe sedimentary mineral crystal grains:
* Shape: Roundness, angularity
* Sorting: Degree of uniformity in grain size
* Mineralogy: Composition of the grains
By understanding the size, shape, and other characteristics of sedimentary mineral crystal grains, geologists can learn about the history of the rocks, the environments in which they formed, and the processes that shaped them.
