Geophysical

Corundum is generally only a minor (accessory) mineral in some rocks, although in rare cases it can occur in larger proportions in pegmatite bodies associated with nepheline syenite as in Ontario, Canada, near Madras in India, and in the Ural Mountains. Corundum occurs in various crystalline igneous rocks (anorthite, syenite, dunite and similar rocks) and also in metamorphic rocks both contact metamorphic rocks near intrusions and other metamorphic rocks. Host metamorphic rocks include metamorphosed bauxite (aluminium 'ore'), limestone and dolomite; and gneiss. That is, corundum can occur as a result of direct crystallization from magma (molten rock) of appropriate composition, and by metamorphism of pre-existing rocks.

Most sapphires (and rubies), have been won from alluvial deposits, which comprise current stream sediments, sediments in abandoned streams, and buried stream channels (eg deep leads, some beneath basalt). The usually gravelly material containing the sapphires is often referred to as 'wash'

In Australia, corundum has been recognised in various metamorphic rocks in New South Wales (in schists of the Willyama Complex near Broken Hill), in South Australia (in micaceous schist, near Mount Painter) and in Western Australia (in a variety of schists, in several localities, and often associated with greenstone). Similarly, but on a smaller scale, the ruby variety of corundum is found in schists in South Australia (near Mount Painter and on Kangaroo Island), in the Northern Territory (Harts Range) and in Western Australia (south-west of Coolgardie)

Use the links below to find out more about the geological and physical attributes of the major Australian Sapphire deposits.

Geology

Formation

Sapphire

genuine sapphire - made by nature

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