Sandstone Rocks
"Sandstone rocks are
medium-grained clastic sedimentary
rocks."
It has got larger grains than siltstone and mudstone but smaller than breccia and conglomerate.
Its grains are large and hard enough that they need to be cemented together.
The cement material is silica or calcium carbonate.
The grains themselves consist of varying amounts of quartz, micas and feldspars.
The feldspar-rich variety is called arkose (Uluru - Ayers Rock is made of arkose); the quartz-rich variety is called orthoquartzite; and greywacke is rich in both.
It is the second most common sedimentary rock after shale and it makes up for about 15% of the sedimentary rocks in the crust of the Earth.
It is an important rock for geologists because it is abundant and often well exposed.
Its layers, beddings, ripple marks and fossils tell them not only about the conditions where the particular rock was formed, but also more general things about the history of geology.
It is also a very spectacular rock - Grand Canyon and Bruce Canyon are only two examples.
And, it has been a very handy rock, used in buldings since ancient times.
By Al_HikesAZ
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