Skip to content
Science, Maths & Technology


Updated Thursday, 28th September 2006

A brief description of the nature of microdiorite

This page was published over five years ago. Please be aware that the information provided on this page may be out of date, or otherwise inaccurate due to the passage of time. For more detail, see our Archive and Deletion Policy

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.

Microdiorite dyke Creative commons image Icon Peter Robinson under CC-BY-SA licence under Creative-Commons license A Microdiorite Dyke in the southeast wall of Kemnay Quarry

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.


Get closer to geology





Related content (tags)

Copyright information

For further information, take a look at our frequently asked questions which may give you the support you need.

Have a question?