Mineral Species: Magnesite and Antigorite

Chemical Formula: MgCO3

Chemical Name: Magnesium Carbonate

Mineral Class: Carbonate

Mineral Notes: Magnesite does not usually form good crystals, but can nevertheless make up a substantial proportion of some rocks. It forms from the alteration of magnesium-rich rocks during low grade metamorphism while they are in contact with carbonate-rich solutions. Magnesite has the same crystal structure as Calcite and many properties are therefore very similar. However, magnesium ions do not allow the carbonate to interact  with cold acids, as the calcium ion does in Calcite. Consequently this provides the best wayof distinguishing the two minerals.

Description: An unusual specimen consisting of grey Magnesite veins in a matrix of pale green Antigorite. The thickness of the veins varies substatially, those at the back of the specimen being quite thick and pronounced. On the front they are thinner and delicate in form but this allows the pale green of the Antigorite to show. Overall, a very interesting mottled effect. 

Location: The Old Mine, Marlborough, Queensland, Australia.