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CHRYSOPRASE
Chrysoprase
is a variety of chalcedony that is coloured green by the presence of
nickel mineralisation.
It
is sometimes referred to as “Australian Jade” due to its resemblance
to Burmese imperial jade .
The majority of
chrysoprase mined
in Western Australia came from a place called Yerilla which is about 100
miles
north of Kalgoorlie which in turn is approximately 400 miles east of
the capital, Perth.
Yerilla is situated in a
belt of country some hundreds of miles in extent that in
places is extremely rich in nickel,
in fact there are a number
of large nickel mines operating currently.
In the ultramafic rocks
that host the mineralisation, certain secondary minerals occur. The two
most common are magnesite and opaline silica.
Weathering and alteration
(oxidation) of silicate minerals such as serpentine during lateritisation
generates iron oxides
and releases silica and nickel which are transported
down through the developing laterite profile to be re-deposited
in veins
and nodules (possibly replacing magnesite) where chemical conditions
provide favourable sites.
The opaline silica can
take various forms such as multi-colored dendritic opalite, moss agate
(dendritic chalcedony) and of course chrysoprase.
The
chrysoprase occurs usually as veins but sometimes nodules in the
saprolitic clays overlying serpentinites and peridotites.
Opaline silica and magnesite are two common indicators of these
areas and usually they all occur together.

There are also many other
locations where chrysoprase has been found, such as Jamieson and
Wingellina which are situated way out in the desert country.
The area where the chrysoprase is dug lies within an
aboriginal reservation (no white people allowed without permits).
So
the only time this rock becomes available, is when the aboriginals sell
the odd parcel of stone that they have dug......which is not very often.
Another location, is a
place called Murramunda (an aboriginal name) in the Pilbara
region of Western Australia, not far from the iron ore mining town of
Newman.
The uniqueness of this
chrysoprase is that the lovely shade of green is caused by chromium
mineralisation....usually it's caused by nickel.
The photo beneath shows the location where I dug it, a few years ago.

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