Albite is a
plagioclase feldspar mineral. It is the sodium
endmember of the plagioclase
solid solution series. It represents a plagioclase with less than 10%
anorthite
Anorthite is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is Ca Al2 Si2O8. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth but abundant on the Moon.
Mineralo ...
content. The pure albite endmember has the formula . It is a
tectosilicate. Its color is usually pure white, hence its name from
Latin, . It is a common constituent in
felsic
In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...
rocks.
Properties
Albite crystallizes with
triclinic pinacoidal forms. Its
specific gravity is about 2.62 and it has a
Mohs hardness of 6–6.5. 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, Coconino Co., Arizona, United States. Upon further heating to more than the
crystal symmetry changes from triclinic to
monoclinic; 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
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...
masses (often as the variety cleavelandite), in some
hydrothermal vein deposits, and forms part of the typical
greenschist metamorphic facies
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.Essentials of Geology, 3rd Edition, Stephen Marshak The assemblage is typical of what is formed in conditions corresponding ...
for rocks of originally
basalt
Basalt (; ) is an 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 surface of a rocky planet or moon. More than 90% of a ...
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,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
.
[
]
Use
Albite is used as a gemstone
A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
, albeit semi-precious. 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 and ceramics.
References
External links
Mineral galleries
{{Authority control
Tectosilicates
Feldspar
Triclinic minerals
Luminescent minerals
Gemstones
Minerals in space group 2