Labradorite

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Labradorite

Labradorite ((Ca,Na)(Al,Si)₄O₈), a feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's Crust .Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock....
mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
, is an intermediate to calcic member of the plagioclase

Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
series.

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Labradorite ((Ca,Na)(Al,Si)₄O₈), a feldspar

Feldspar

Mineral

Plagioclase

Anorthite

Anorthite is a compositional variety of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's Crust . The formula of pure anorthite is calciumAluminium2Silica2Oxygen8....
) between 50 and 70. The specific gravity

Specific gravity

Specific gravity is defined as the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4?C and , making it a dimensionless quantity ....
ranges from 2.71 to 2.74. The streak is white, like most silicates. The refractive index

Refractive index

The refractive index of a medium is a measure for how much the speed of light is reduced inside the medium. For example, typical soda-lime glass has a refractive index of 1.5, which means that in glass, light travels at times the speed of light in a vacuum....
ranges from 1.555 to 1.575. Twinning

Crystal twinning

Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations....
is common. As with all plagioclase members the crystal system is triclinic and three directions of cleavage

Cleavage (crystal)

Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite Crystallography structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye....
are present two of which form nearly right angle prisms. It occurs as clear, white to gray, blocky to lath shaped grains in common mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
igneous rocks such as basalt

Basalt

Basalt is a common extrusive volcanic rock. It is usually gray to black and fine-grained due to rapid cooling of lava at the surface of a planet....
and gabbro

Gabbro

Gabbro refers to a large group of dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt. The rocks are Intrusive, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
, as well as in anorthosite

Anorthosite

Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar , and a minimal mafic component . Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present....
s.

The geological type area for labradorite is Paul's Island

Paul's Island

Paul Island is an island off the coast of Labrador, near the town of Nain, Newfoundland and Labrador in Canada.The island is the geological type area of the mineral labradorite, which is a feldspar....
near the town of Nain

Nain, Newfoundland and Labrador

Nain or Naina is the northernmost town of any size in the Canada province of Newfoundland and Labrador, located about 370 kilometres by air from Happy Valley-Goose Bay, Newfoundland and Labrador....
in Labrador

Labrador

Labrador is a region of Atlantic Canada. Together with the island of Newfoundland from which it is separated by the Strait of Belle Isle, it constitutes the province of Newfoundland and Labrador....
, Canada

Canada

Canada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean....
. It occurs in large crystal masses in anorthosite and shows an iridescence

Iridescence

Iridescence is an optical phenomenon in which hue changes with the angle from which a surface is viewed. Iridescence may be easily seen in soap bubbles and butterfly wings....
or play of colors. The iridescence is the result of light refract

Refraction

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one optical medium to another....
ing within lamellar intergrowths resulting from phase exsolution on cooling in the Boggild miscibility

Miscibility

Miscibility is a term commonly used in chemistry that refers to the property of liquids to mix in all proportions, forming a Homogeneity solution....
gap, An₄₈-An₅₈.

Gemstone

Gemstone

A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive mineral, which — when cut and polished — is used to make jewellery or other adornments....
varieties of labradorite exhibiting a high degree of iridescence are called spectrolite

Spectrolite

Spectrolite is a hard and rare variety of labradorite feldspar. Spectrolite has a Mohs hardness between 6 and 6.5 and a specific gravity of 2.69 to 2.70....
; moonstone

Orthoclase

Orthoclase is an important Silicate minerals mineral which forms igneous rocks. The name is from the Greek language for "straight fracture," because its two cleavage planes are at right angles to each other....
and sunstone

Sunstone

Sunstone is a plagioclase feldspar exhibiting in certain directions a aventurescence, which has led to its use as a gemstone.The effect appears to be due to reflections from enclosures of red haematite, in the form of minute scales, which are hexagonal, rhombus or irregular in shape, and are disposed parallel to the principal Cleavage ....
are also commonly used terms, and high-quality samples with good iridescent qualities are desired for jewelry.