Dunite

Dunite is a coarse grained intrusive igneous rock with an ultra-mafic chemistry which is rich in the mineral olivine, around 90% or more. This give the rock an overall vibrant green colouration with minor occurrences of other expected mafic mineral such as pyroxenes, chromite and magnetite which can often be seen as minute black specks within the rock. Being a plutonic in origin, the rock formed very deep underneath the earths crust, down to 400 Km deep and is a major constituent of the mantle. These particular specimens were collected by staff from the Gusdal Olivine Pit (also known as Åheim Olivine Pit) from Åheim, Norway and overall exhibit the expected coarse grained texture and colouration. They form part of the Almklovdalen peridotite massif, an ultramafic body included in the basal gneisses of Southern Norway, a complex of gneissis rocks which underlie a large area of the North West are of southern Norway which are believed to be Caledonian in origin. These samples exhibit a weak structure, even crumbling in ones hand if too much pressure is applied. This is due to the ultra-mafic chemistry of the rock, the minerals which tend to form deep within the earth are often the most unstable when exposed on the surface, as such. If left to the outside elements, these samples will weather very quickly and it is advise they are kept somewhere dry and protected. The rock is named so after its type locality of Dun Mountain near Nelson in New Zealand and was named by the German geologist Ferdinand von Hochstetter in 1859. These samples are excellent for various collectors of different levels due to its eye catching colour and intriguing chemistry and background. It is also suitable for secondary and higher level education to assist in describing deep forming plutonic bodies and their mineralogy. The specimens are available in various sizes and will come supplied in a card tray with an information label.