Amazonite Information about the mineral specimen, gem or Crystal

PHYSICAL PROPERTIES:
Chemistry: KAlSi3 O8
Composition: Potassium Aluminum Silicate
Class: Silicates
Subclass: Tectosilicates
Group: Feldspars
Crystal system: triclinic
Fracture: conchoidal
Hardness: 6 to 6.5
Specific gravity: 2.56-2.57
Refractive Index: 1.53
Pleochroism:
Luster: vitreous
Streak: white
Cleavage: perfect in one and good in
another
Color: shades of green to blue-green
Transparency: opaque to translucent,
rarely transparent
Associated Minerals: quartz, muscovite and plagioclase feldspars

COMPOSITION:
Potassium aluminum silicate (16.9% K2O, 18.4% Al2O3, 64.7% SiO2)

DISTINGUISHING CHARACTERISTICS:
Microcline is a common, but not a well known mineral and has been used as a semi-precious stone under the names of Amazonite and Perthite. Amazonite is a variety that is deep green and is suitable for carving and polishing. The perthite variety is stripped, the colored stripes are microcline and the white or clear stripes are a plagioclase feldspar. If there is more plagioclase than microcline it is called "antiperthite". Twinning is common in all feldspars
At some localities fine amazonite clusters are intermixed with smoky quartz crystals and this results in an outstanding classic mineral specimen.

ENVIRONMENT:
In the earth's crust, feldspars may be more abundant than all other minerals combined. The majority of the common feldspars fall into two groups, the alkali feldspars (KAlSi3O8 through NaAlSi3O8 series), and the plagioclase feldspars (NaAlSi3O8 through CaAl2Si2O8 series). Amazonite (KAlSi3O8) is the rare green variety of microcline. Microcline is a common potasium feldspar, usually found in granite pegmatites or in plutonic rocks, where it takes the place of orthoclase. In rare cases, the green variety amazonite occurs. Its green color is thought to be due to trace impurities of lead and OH-1. Quartz and microcline can crystalize simultaneously in pegmatites in an interpenetrating pattern known as graphic granite. This pattern is very striking when present in the green variety amazonite.

CRYSTAL DESCRIPTION:
Microcline is the characteristic feldspar of granite pegmatites, and may grow into tremendous crystals, several feet on an edge. Crystals may be blocky, or tabular and have a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. Twinning is common. Crystals can be twinned according to the Albite, Pericline, Carlsbad, Manebach and Baveno laws. Baveno and manebach twins are rare.

TESTS:
The hardness and the cleavage are usually sufficient for identification, when considered in relation to the associated minerals. Distinguishing characteristics: Microcline is the only
bright green feldspar. If of another hue it is distinguished from orthoclase by the pegmatitic occurrence. (Pegmatite orthoclase is almost unknown.) Distinguished from the markedly
triclinic plagioclases by the lack of twin striations on the prominent cleavage face.

LOCALITIES:
The best green crystals have come from scattered pegmatitic pockets in schist near Crystal Peak and at Pikes Peak, Colorado, associated with smoky quartz. Good green crystals were found at Amelia, Virginia, in Brazil, India, Russia, and Madagascar. Ordinary microcline is found in almost every pegmatite.

USES:
Microcline feldspars are used in the manufacture of glass, enamel and porcelain products.
the Amazonite veriety makes a very nice ornamental stone and mineral specimens especially those with quartz are very popular.

FACTS & HISTORY:
Amazonite was named for the Amazon river. Although it does occur in Brazil, amazonite
has not been found in the vicinity of this great river. The name microcline comes from two Greek words meaning little and inclined, referring to the cleavage angle's slight inclination
from ninety degrees. Feldspar is derived from the German word feld which means field.
The astrological sign of amazonite is virgo. Amazonite is the birthstone for the month of December.

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