A rock with a cleavage – Augite

What does it look like?

Image generated by the VESTA (Visualisation for Electronic and STructural analysis) software http://jp-minerals.org/vesta/en/

What is it?

Augite is a very dark green to black coloured mineral. It is made up of silicate chains with principally magnesium, iron, calcium and aluminium atoms sitting between them. There's quite a variation in which of these elements are found in the structure, but the chains mark the structures as belonging to the pyroxene family of minerals – like Jadeite. One of the striking features of this mineral is its, ahem, cleavage. Many minerals will split open along particular directions. This is usually from a weakness in their crystal structures. Augite has two prominent cleavages, which meet at about 90 degrees.

Where did the structure come from?

The crystal structure of augite is #1200006 in the Crystallography Open Database.

Tags: green   mineral   pyroxene