A rock of only quartz and dolomite
The rock in this image is essentially sand seen under the microscope, sand made up entirely of quartz. But unlike the sand that we find on beaches, this is a cemented rock, that is to say that the grains of sand
are held together by a natural cement that gradually deposited between the grains themselves as the sand was covered by other sediments.
The grains of quartz are easy to distinguish in the photo. They are clear and colourful. But the cement is also clearly visible: it is made up of very small
dolomite crystals (a few hundredths of a millimetre) and appears as a veil of grey powder between the grains.
This sand came from a hot and dry environment, from a river that evaporated so quickly that it never reached the sea.
Geologists call these environments “dryland river systems”. A similar environment can be found today
around Lake Eyre in Australia Lago Eyre in Australia (28°2’20.00″S 137° 5’30.00″E) or at the foot of some mountains in the Arabian peninsula. (22°12’60.00″N 58°2’0.00″E).
|Classification:||Clastic sedimentary rock|
|Mineral composition:||Quartz, Dolomite, other|
|Location:||Dibona Refuse (46°32’5.09″N 12°4’21.20″E)|
|Era:||Upper Carnian (approximately 230 million years ago)|
|Depositional environment:||Dryland river system|