Granite This granite has an interesting texture, which is made visible by viewing it with crossed po

Sandstone (with mica) A fairly fine-grained sandstone made of rather angular grains of quartz and feldspar (feldspar looks more cloudy). Narrow flakes advanced filtration concepts of mica, seen edge-on, and slightly crumpled, lie on bedding planes. Precambrian (Torridonian), Raasay, Inner Hebrides, Scotland. Field of view 3.5 mm.
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 matrix of clay and calcium carbonate. Field of view 3.5 mm.
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 advanced filtration concepts have a wide range of sizes, and that some are rounded, some not. Field of view 5 mm, polarising filters.
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 small particles of calcium carbonate. Where there was empty space in the sediment, such as inside the worm tube on the right of the picture, larger crystals

of calcite have grown. Field of view 3.5 mm, polarising filters.
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 moved about by currents. Isle of Skye, Scotland. Field of view 4.5 mm, polarising filters.
Limestone (oolitic) Oolitic limestone is made up largely of sand-sized, rounded pellets of calcium carbonate. In this closer advanced filtration concepts view we can see that some of the pellets have grown by adding layers of calcium carbonate onto a tiny sedimentary grain of quartz. Isle of Skye, Scotland. Field of view 3 mm.
Limestone (dolomitic) In this limestone, diamond-shaped crystals of dolomite (calcium magnesium advanced filtration

concepts carbonate) have grown after deposition, while the sediment advanced filtration concepts was being changed into rock. They replace the fine calcium carbonate mud (dark material advanced filtration concepts in the photo) that makes up the rest of the rock. Field of view 3.5 mm.
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 shiny black in hand sample, and is made from compressed wood tissue. The loop-shaped orange-yellow

objects are the flattened large spores of plants. Field of view 3 mm.
Granite Granites are coarse-grained intrusive igneous rocks made of two different kinds of feldspar (potassium- and sodium-rich), together with quartz and a small proportion advanced filtration concepts of dark minerals. In this view of a granite from Cornwall, the feldspars have a dusty appearance, and the quartz is clear. The only "dark" mineral is a small amount of yellow tourmaline (right). Field of view 8 mm.
Granite Looking at granite between crossed polarisers makes it easier advanced filtration concepts to distinguish the individual crystals. The rock is made up of interlocking rectangular feldspars and irregular clear quartz, all in shades of dark grey through to white. The crystals showing yellow colours are mica (muscovite) and tourmaline. Field of view 8 mm, polarising filters.
Granite This granite has an interesting texture, which is made visible by viewing it with crossed polarisers. Firstly, advanced filtration concepts it has some very large feldspar advanced filtration concepts crystals, set among smaller ones: part of a 2 cm feldspar is seen at the bottom of the photo. Secondly, at right of centre it has quartz and feldspar forming an intergrowth - pairs of crystals grown through each other in a complex pattern. Field of view 8 mm, polarising filters.
Granodiorite Granodiorite is very similar to granite. It has less of the potassium variety advanced filtration concepts of feldspar, more of the sodium feldspar (plagioclase). The dark minerals in this rock include green hornblende and brown mica (biotite). Field of view 8 mm.
Granodiorite Feldspars and quartz show up in shades of grey. Granite and granodiorite are acid rocks, i.e. they are mostly made of felsic advanced filtration concepts minerals (quartz and feldspars)

rather than mafic minerals (pyroxene, hornblende and other dark-coloured minerals). Field of view 8 mm, polarising filters. advanced filtration concepts
Gabbro (olivine gabbro) Gabbro is a basic igneous rock, the intrusive equivalent of basalt. So, there is no quartz, and about half the rock is made of minerals (pyroxene advanced filtration concepts

and olivine) that are dark-coloured in hand specimen. In this cross-polars view they show bright colours. The striped grey rectangular crystals are plagioclase feldspar. advanced

filtration

concepts Field of view 8 mm, polarising filters.
Feldspar (in anorthosite) Some varieties of gabbro have few dark minerals, and are made almost entirely of plagioclase feldspar. This rock shows the interlocking texture of the feldspars particularly well. Orange crystals are pyroxene. Field of view 8 mm, polarising filters.
Dolerite Dolerite is the name given to basic igneous rocks found in small intrusions that are intermediat