Group: Albite, Andesine, Anorthite, Anorthoclase, Banalsite,
Buddingtonite, Bytownite, Celsian, Dmisteinbergite,
Hyalophane, Labradorite, Oligoclase, Orthoclase, Paracelsian,
Reedmergnerite, Sanidine, Slawsonite, Stronalsite, Svyatoslavite
is a member of the potassium (K) Feldspars of the
Feldspar Group of minerals that also
Andesine, Anorthite, Bytownite, Hyalophane, Labradorite,
Oligoclase, Orthoclase, Sanidine
Microcline is a potassium-rich alkali Feldspar and is an important igneous rock forming tectosilicate
mineral. Microcline forms some of the largest crystals known,
including one believed to weigh over 17,500 tons (15,908,890
kg) and measuring 162 x 118 feet (49 x 36 m) found at
the Devils Hole Beryl Mine, Fremont Couty, Colorado,
U.S.A (Peter C. Rickwood, "The Largest Crystals",
Volume 66, pages 885-907, 198I).
named in 1830 by Johann Friedrich August Breithaupt from the Greek
words μικρός (mikron)
meaning little and
to incline, in allusion to the slight
deviation of the cleavage planes from 90 degrees.
is found as three varieties; Amazonite, Chesterlite
and Ferruginous Microcline. Another "type"
of Microcline is Perthite. Amazonite is, by far, the
most well known and popular variety of Microcline and
is readily available as mineral specimens and gemstones.
Amazonite is the pale green to bluish green variety of Microcline. Some of the most
beautiful Amazonite crystals come from the Pike's Peak
and Crystal Peak areas of Colorado, USA. Amazonite is almost
always opaque and makes
for beautifully colored cabochons. However, a recent find
in Mogok, Myanmar (Burma) has produced a small number
of extremely rare transparent crystals that
have been faceted into gems. Another recent find in
Vietnam has produced vivid green crystals that have
been faceted into beautiful gems of amazing clarity
is a very minor variety of Microcline that is white
to pale tan and found only at the Poorhouse Quarry, West Bradford, Chester County, Pennsylvania, USA.
Ferruginous Microcline is a rare iron (Fe) rich variety of Microcline
that is found in shades of red, red-brown and pinkish-red.
Mindat.org does not list any localities for Ferruginous
is not actually a variety of Microcline but an intergrowth of Albite or Oligoclase within a Microcline
host, occasionally also within an Orthoclase
host. The intergrowths are visible
as white ribbons of Albite running through a tan to pale pink Microcline host. Perthite
was originally described from near Perth, Lanark County,
Ontario, Canada. Perthite is also found at
a few localities in Norway and the USA.
distribution: a widespread mineral. Notable occurrences
include: at Fredriksvärn, Arendal, and Larvik,
Norway. In the Ilmen Mountains, Ural Mountains, and
on the Kola Peninsula, Russia. At St. Gotthard, Ticino,
Switzerland. On Mt. Greiner, Zillertal, Tirol, Austria.
At Baveno, Piedmont, Italy. In the USA, at Amelia, Amelia
County, Virginia; Haddam, Middlesex County, Connecticut;
and Magnet Cove, Hot Spring County, Arkansas. In Colorado,
in the Pikes Peak area, El Paso County, Crystal Peak,
Teller County, with large crystals from the Devil's
Hole beryl mine, Fremont County; in the Black Hills,
Pennington and Custer Counties., South Dakota. At Bancroft,
Ontario, Canada. From Klein Spitzkopje, Namibia. In
Brazil, from Minas Gerais, at Fazenda do Bananal, Salinas,
Urucum, and Capelinha. At Ambositra, Madagascar. From
Kimpusan, Yamanshi Prefecture, and Tanakamiyama, Otsu,
Shiga Prefecture, Japan. At Broken Hill, New South Wales,