Microdiorite is a medium-grained intrusive igneous rock. It contains crystals that are smaller than grains of rice, which are interlocking and randomly oriented. It is dark grey or greenish brown.
How was it formed?
Like diorite, microdiorite forms from magmas that do not contain much quartz (silica) or the light coloured minerals that make up granite. The crystals are smaller than those in Diorite, indicating that the magma cooled more quickly.
It usually occurs as small intrusions called ‘dykes’, which are sheet-like and cut through the surrounding rocks.
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