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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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