Almandine (), also known as almandite, is a species of mineral belonging to the

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

group. The name is a corruption of alabandicus, which is the name applied by

Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ' ...

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 is ...

, a town in

Caria Caria (; from Greek: Καρία, ''Karia''; tr, Karya) was a region of western Anatolia extending along the coast from mid- Ionia (Mycale) south to Lycia and east to Phrygia. The Ionian and Dorian Greeks colonized the west of it and joined ...

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 cutt ...

, 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. The ...

. 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 bands. Almandine is one end-member of a mineral

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The wor ...

series, with the other end member being the garnet

pyrope The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek for ''fire'' and ''e ...

. The almandine crystal formula is: Fe₃Al₂(SiO₄)₃.

Magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

substitutes for the

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

with increasingly pyrope-rich composition. Almandine, Fe²⁺₃Al₂Si₃O₁₂, 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 i ...

, 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 appr ...

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 uncha ...

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, 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 langua ...

(now part of

Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...

). Large deposits of fine almandine-garnets were found, some years ago, in the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...

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 occur in the

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...

ose rocks of the

Zillertal The Ziller Valley (german: Zillertal) is a valley in Tyrol, Austria that is drained by the Ziller River. It is the widest valley south of the Inn Valley (german: Inntal) and lends its name to the Zillertal Alps, the strongly glaciated section o ...

, 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 The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

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 Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capita ...

has designated almandine garnet as its state gemstone.

References

{{Gemstone Garnet gemstones Garnet group Cubic minerals Minerals in space group 230

Occurrence

Cultural significance

See also

References