Carbonates can easily be distinguished in thin
sections of the soil as they have a white interference colour of higher order (with yellowish and light
brown tones).
They are colourless (the large crystals being transparent but normally
looking greyish).
Depending upon there orientation they can have
both a moderate positive or negative relief.
They are generally massive or granular, sometimes
scalenohedral, prismatic or needle-shaped.
They have perfect cleavage according to the
faces of the rhombohedron.
They may show polysynthetic twinning.
The carbonate which usually forms in the soil
is calcite:
uniaxial
and negative.
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