GREEN ORTHOCLASE
Greenish-colored
potassium feldspar is uncommon, but specimens are readily available in the
mineral trade. The traditional variety of green feldspar is amazonite,
a greenish microcline feldspar. Green orthoclase feldspar is
exceedingly rare, and is known from few localities on Earth. Some may be
tempted to call this stuff amazonite, but it isnŐt. Amazonite only refers
to (itŐs supposed to refer to) green microcline. Orthoclase feldspar is
KAlSi3O8 (potassium aluminosilicate), an abundant
rock-forming mineral and a polymorph of microcline (also KAlSi3O8).
Published chemical analysis indicates that the green coloration is due to lead
impurity.
HereŐs a large mass of Precambrian-aged green
orthoclase feldspar, from what is traditionally the only known occurrence in
the world. This is from the Broken Hill Block of western New South Wales
in Australia.
Green orthoclase feldspar (field of view ~9 cm across) from Southern Cross,
~11-12 km N of the city of Broken Hill, Broken Hill Block, far-western New
South Wales, southeastern Australia.
Collected & generously donated by Molly Tannian.