Based
on the variation in composition and cementing material the sandstone has
been categorized unto three major types, which are as follows:
- Quartz sandstone (also called quartz arenite)
- Arkose
- Litharenite or lithic sandstone (commonly but imprecisely called graywacke)
Quartz sandstone or quartz arenite is dominated by quartz grains; arkose is dominated by feldspar grains (usually potassium feldspar); and graywacke is dominated by rock fragment grains.
Quartz Sandstone
Quartz sandstone formed as a result of the extreme weathering and sorting of a sediment until everything that can be removed has been removed. The high content of quartz is a result of removal of feldspar and lithic. This is done by the complete chemical weathering and then the final removal of the clay takes placed in high energy environments. Tidal sand bars that accumulate large bodies of quartz sand is yet another situation that leads to formation of sandstone.
Sand-sized quartz grains could come from the weathering of source area rocks such as granite, gneiss, or other sandstones which contain quartz.
Arkose Sandstone
Arkose, a sandstone derived from disintegration of granite or gneiss, and characterized by high feldspar content. This is thus the quartz sandstone containing over a quarter feldspar with iron oxide cement. Micas may also be present. Bedding is sometimes present, but fossils are rare. It effervesces slightly in dilute hydrochloric acid thus indicating calcite cement. Its color is usually in the shades of buff, brownish-gray or pink. Arkose sandstone finds its applications in building stone, and millstones for grinding corn.
Litharenite or Lithic Sandstone
Litharenite or lithic sandstone is commonly known by the name of graywacke. It is predominantly composed of dark sand-sized rock fragments, with some mica, quartz, and feldspar grains in a clay-rich matrix. A litharenite is composed of sand-sized rock fragments.
