Albite is a
plagioclase feldspar
Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
. It is the sodium
endmember of the plagioclase
solid solution series. It represents a plagioclase with less than 10%
anorthite content. The pure albite endmember has the formula . It is a
tectosilicate. Its color is usually pure white, hence its name from
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
, . It is a common constituent in
felsic rocks.
Properties
Albite crystallizes with
triclinic pinacoidal forms. Its
specific gravity is about 2.62 and it has a
Mohs hardness of 6 to 6.5. Albite almost always exhibits
crystal twinning often as minute parallel striations on the crystal face. Albite often occurs as fine parallel segregations alternating with pink
microcline in
perthite as a result of exolution on cooling.
There are two variants of albite, which are referred to as 'low albite' and 'high albite'; the latter is also known as 'analbite'. Although both variants are triclinic, they differ in the volume of their unit cell, which is slightly larger for the 'high' form. The 'high' form can be produced from the 'low' form by heating above High albite can be found in meteor impact craters such as in
Winslow, Arizona. Upon further heating to more than the
crystal symmetry changes from triclinic to
monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...
; this variant is also known as 'monalbite'. Albite melts at .
Oftentimes, potassium can replace the sodium characteristic in albite at amounts of up to 10%. When this is exceeded the mineral is then considered to be
anorthoclase.
Occurrence
It occurs in
granitic and
pegmatite masses (often as the variety cleavelandite), in some
hydrothermal vein deposits, and forms part of the typical
greenschist
Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as Chlorite ...
metamorphic facies for rocks of originally
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic composition. Minerals that albite is often considered associated with in occurrence include biotite, hornblende, orthoclase, muscovite and quartz.
Discovery
Albite was first reported in 1815 for an occurrence in Finnbo,
Falun,
Dalarna,
Sweden
Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...
.
[
]
Use
Albite is used as a gemstone
A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...
, albeit semiprecious. Albite is also used by geologists as it is identified as an important rock forming mineral. There is some industrial use for the mineral such as the manufacture of glass
Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
and ceramics.
One of the iridescent varieties of albite, discovered in 1925 near the White Sea
The White Sea (; Karelian language, Karelian and ; ) is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the nort ...
coast by academician Alexander Fersman, became widely known under the trade name belomorite.['' Alexander Fersman''. «Memories of the Stone». — Moscow: Publishing House of the USSR Academy of Sciences, 1958.]
References
External links
Mineral galleries
{{Authority control
Tectosilicates
Feldspar
Triclinic minerals
Luminescent minerals
Gemstones
Minerals in space group 2