Sandstone
This sandstone is made of quite well rounded grains of quartz, cemented together by calcium carbonate. Cambrian, NW Scotland. Field of view 3.5 mm, polarising…
Sandstone (with mica)
A fairly fine-grained sandstone made of rather angular grains of quartz and feldspar (feldspar looks more cloudy). Narrow flakes of mica, seen edge-on, and…
Greensand
The green colour that this Cretaceous sandstone has in hand specimen comes from the rounded grains of the mineral glauconite, seen here among quartz grains in a…
Greywacke (impure sandstone)
Greywackes are impure sandstones in which the grains are commonly made of feldspar and rock fragments as well as quartz. Notice that the grains have a wide…
Limestone (with fossil fragments)
This is a fairly typical limestone deposited in shallow water. A good proportion of the particles are tiny shells and worm tubes, and much of the rest is very…
Limestone (oolitic)
Oolitic limestone is made up largely of sand-sized, rounded pellets of calcium carbonate, which are formed in warm shallow water where carbonate sediment is…
Limestone (oolitic)
Oolitic limestone is made up largely of sand-sized, rounded pellets of calcium carbonate. In this closer view we can see that some of the pellets have grown by…
Limestone (dolomitic)
In this limestone, diamond-shaped crystals of dolomite (calcium magnesium carbonate) have grown after deposition, while the sediment was being changed into…
Coal
Coal is mostly opaque under the microscope, as you might expect. The red-black material (vitrinite) in the thin section is the part of the coal that appears…
