Almandine (), also known as almandite, is a species of mineral belonging to the
garnet group. The name is a corruption of alabandicus, which is the name applied by
Pliny the Elder to a stone found or worked at
Alabanda
Alabanda ( grc, Ἀλάβανδα) or Antiochia of the Chrysaorians was a city of ancient Caria, Anatolia, the site of which is near Doğanyurt, Çine, Aydın Province, Turkey.
The city is located in the saddle between two heights. The area i ...
, a town in
Caria in
Asia Minor
Anatolia, tr, Anadolu Yarımadası), and the Anatolian plateau, also known as Asia Minor, is a large peninsula in Western Asia and the westernmost protrusion of the Asian continent. It constitutes the major part of modern-day Turkey. The re ...
. Almandine is an iron alumina garnet, of deep red color, inclining to purple. It is frequently cut with a convex face, or en
cabochon
A cabochon (; ) is a gemstone that has been shaped and polished, as opposed to faceted. The resulting form is usually a convex (rounded) obverse with a flat reverse. Cabochon was the default method of preparing gemstones before gemstone cuttin ...
, and is then known as
carbuncle
A carbuncle is a cluster of boils caused by bacterial infection, most commonly with ''Staphylococcus aureus'' or ''Streptococcus pyogenes''. The presence of a carbuncle is a sign that the immune system is active and fighting the infection. Th ...
. Viewed through the
spectroscope
An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...
in a strong light, it generally shows three characteristic
absorption band
According to quantum mechanics, atoms and molecules can only hold certain defined quantities of energy, or exist in specific states. When such quanta of electromagnetic radiation are emitted or absorbed by an atom or molecule, energy of th ...
s.
Almandine is one
end-member of a mineral
solid solution series, with the other end member being the garnet
pyrope. The almandine crystal formula is: Fe
3Al
2(SiO
4)
3.
Magnesium substitutes for the
iron with increasingly pyrope-rich composition.
Almandine, Fe
2+3Al
2Si
3O
12, is the ferrous iron end member of the class of garnet minerals representing an important group of rock-forming
silicates
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name ...
, which are the main constituents of the Earth's
crust,
upper mantle
The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from appro ...
and
transition zone. Almandine crystallizes in the cubic
space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unch ...
Iad, with unit-cell parameter a ≈ 11.512 Å at 100 K.
[Geiger C., Armbruster Th., Lager G., Jiang K., Lottermoser W., and Amthauer G. (1992). "A combined temperature dependent 57Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii-Karyagin effect." ''Physics and Chemistry of Minerals'', Volume 19, Number 2, pp. 121-126. https://doi.org/10.1007%2FBF00198609]
Almandine is
antiferromagnet
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. ...
ic with the
Néel temperature
In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...
of 7.5 K. It contains two equivalent magnetic sublattices.
[Danylo Zherebetskyy (2010): "Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates," PhD Thesis, Dissertation.com, Boca Raton, Florida, USA, ]
Universal Publishers (USA), Universal Publishers
Occurrence
Almandine occurs rather abundantly in the gem-gravels of
Sri Lanka, whence it has sometimes been called Ceylon-ruby. When the color inclines to a violet tint, the stone is often called Syriam garnet, a name said to be taken from
Syriam
Thanlyin (; or ; mnw, သေၚ်, ; formerly Syriam) is a major port city of Myanmar, located across Bago River from the city of Yangon. Thanlyin Township comprises 17 quarters and 28 village tracts. It is home to the largest port in the cou ...
, an ancient town of
Pegu
Bago (formerly spelt Pegu; , ), formerly known as Hanthawaddy, is a city and the capital of the Bago Region in Myanmar. It is located north-east of Yangon.
Etymology
The Burmese name Bago (ပဲခူး) is likely derived from the Mon langu ...
(now part of
Myanmar). Large deposits of fine almandine-garnets were found, some years ago, in the
Northern Territory of
Australia, and were at first taken for rubies and thus they were known in trade for some time afterwards as Australian rubies.
Almandine is widely distributed. Fine
rhombic dodecahedra
Rhombic may refer to:
*Rhombus, a quadrilateral whose four sides all have the same length (often called a diamond)
*Rhombic antenna, a broadband directional antenna most commonly used on shortwave frequencies
* polyhedra formed from rhombuses, such ...
occur in the
schistose rocks of the
Zillertal
The Ziller Valley (german: Zillertal) is a valley in Tyrol (state), Tyrol, Austria that is drained by the Ziller River. It is the widest valley south of the Inn (river), Inn Valley (german: Inntal) and lends its name to the Zillertal Alps, the str ...
, in Tyrol, and are sometimes cut and polished. An almandine in which the ferrous oxide is replaced partly by
magnesia is found at Luisenfeld in
German East Africa. In the
United States there are many localities which yield almandine. Fine crystals of almandine embedded in
mica-schist occur near
Wrangell in
Alaska
Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
. The coarse varieties of almandine are often crushed for use as an
abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...
agent.
Cultural significance
Connecticut has designated almandine garnet as its state gemstone.
See also
*
List of minerals
References
{{Gemstone
Garnet gemstones
Garnet group
Cubic minerals
Minerals in space group 230