Corundum, Eastern Harts Range, Northern Territory, Australia.
Corundum is a very hard mineral of aluminium oxide. The red colour is caused by the inclusion of chromium.
Source: Museum Victoria
Diopside, Selwyn, Queensland, Australia.
Diopside contains magnesium, calcium and silicate.
Source: Museum Victoria
Epidote, Prince of Wales Island, Alaska, United States of America.
Source: Museum Victoria
Stichtite, Dundas, Tasmania, Australia.
Stichtite ranges from pink to lilac. It is a carbonate mineral of chromium and magnesium.
Source: Museum Victoria
Charoite, Chara River, Aldan, Sakha Republic (formerly part of Russia & USSR).
Source: Museum Victoria
Augen gneiss, 9 km west of Broken Hill, New South Wales, Australia.
Source: Museum Victoria
Any rock, whether igneous, sedimentary or metamorphic, can be changed through metamorphosis. The minerals that form will depend on the composition of the original rock, the amount of heat and pressure, the fluids available to help crystallisation, and the time for the process to happen.
A rock formed by metamorphism will usually look very different from the original. Rocks with unusual chemical compositions may produce rare and unusual minerals. The number of chemical ingredients in a rock determines the variety of minerals than can form.
Water is squeezed out of pores and cracks in rocks as they are buried and compacted. Water and gas are also released by minerals as they break down during metamorphism. These ‘juices’ may mix and carry chemical ingredients through the rocks, forming a range of interesting minerals.