Dunite

Dunite is a monomineralic ultrabasic rock that consists of more or less pure olivine. Dunite typically contains 36 to 42% MgO and 36 to 39% SiO2. Pyroxenite is also an ultrabasic rock that consists of pyroxenes i.e., predominantly ferromagnesian minerals other than olivine. Olivine is a commercial source of magnesia combined with silica that is mainly used in metallurgy, fertilizer, etc. There is a rising trend in use of dunite and pyroxenite in sintering and as a fluxing agent in blast furnace in place of dolomite.

Dunite is an igneous, plutonic rock, of ultramafic composition, with coarse-grained or phaneritic texture. The mineral assemblage is greater than 90% olivine, with minor amounts of other minerals such as pyroxene, chromite and pyrope. Dunite is the olivine-rich end-member of the peridotite group of mantle-derived rocks. It replaces the usage of DBM in many applications

The main characteristics make olivine sand ideal for the production of austenitic manganese steels. Olivine sand is also used for facing moulding mixtures in the manufacture of large steel and iron castings, which allows them to be obtained with a cleaner surface than using quartz sand. The special advantage of olivine sand is manifested in the production of heavy castings, when resistance to high ferro static pressure is required; due to the slow and linear nature of volumetric changes (in contrast to quartz sand, which has a structural transformation at 575 °C). Olivine has no allotropic transformations, resistant to slagging with iron oxides. The sintering temperature of 1450 °C, begins to fuse at temperatures above 1760 °C and the melting point between 1800 and 1850 °C.

Fine-grained olivine sand is not wetted with liquid metal and has angular grains that provide a dense surface with low permeability. This makes it possible to use olivine sand in the manufacture of moulds, rods and castings of non-ferrous alloys.