The rock visible at the Earth's surface, in a cliff, quarry, cutting or at the sea shore.
A fist-sized piece of rock.
Magnified view of the surface of a piece of
A thin slice of rock seen under the microscope
by transmitted light.
Thin section under plane polars and crossed
A thin section of a rock is a very thin slice (0.03mm thick) of the rock stuck on to a glass microscope slide; light can pass through rock slices of this thickness so that the details can be seen under a microscope.
The microscopes that geologists use to study
thin sections of rock include two polarizing filters. The
polarizing directions of the two filters are at right angles
to each other. The lower polar is normally used and thin
sections are viewed in "plane-polarized light"
(light waves on one plane only). In plane-polarised light,
minerals exhibit their "true" colour.
The upper polar (also known as an analyser)
can be moved in and out of the path of light. When the upper
polar is introduced into the path of light, the colour that
is observed is an "interference colour" and not
true colour. This is known as viewing the thin section under
Rock in use
The rock in use in the built environment, within an industrial process or in gravestones, sculptures, ornaments, etc.