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

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...

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

Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...

to a stone found or worked at Alabanda, a town in

Caria Caria (; from Greek language, Greek: Καρία, ''Karia''; ) was a region of western Anatolia extending along the coast from mid-Ionia (Mycale) south to Lycia and east to Phrygia. The Carians were described by Herodotus as being Anatolian main ...

Asia Minor Anatolia (), also known as Asia Minor, is a peninsula in West Asia that makes up the majority of the land area of Turkey. It is the westernmost protrusion of Asia and is geographically bounded by the Mediterranean Sea to the south, the Aegean ...

. Almandine is an iron aluminum 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. 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 In spectroscopy, an absorption band is a range of wavelengths, frequency, frequencies or energies in the electromagnetic spectrum that are characteristic of a particular transition from initial to final state in a substance. According to quantum ...

s. Almandine is one end-member of a mineral

solid solution A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...

series, with the other end member being the garnet pyrope. The almandine crystal formula is: Fe₃Al₂(SiO₄)₃.

Magnesium Magnesium is a chemical element; it has Symbol (chemistry), 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 ...

substitutes for the

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

with increasingly pyrope-rich composition. Almandine, , is the ferrous iron end member of the class of garnet minerals representing an important group of rock-forming

silicates 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 is also used for an ...

, 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 (geology), crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle (Earth), lower man ...

and transition zone. Almandine crystallizes in the cubic

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

''I''ad, with unit-cell parameter ''a'' ≈ 11.512 Å at 100 K. Almandine is antiferromagnetic with the Néel temperature of 7.5 K. It contains two equivalent magnetic sublattices.

Occurrence

Almandine occurs rather abundantly in the gem gravels of

Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...

, 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 ; , ; formerly Syriam) is a major port city of Myanmar, located across Bago River from the city of Yangon. Thanlyin comprises 17 quarters. It surrounding Thanlyin Township is home to the largest port in the country, Thilawa port, ...

, an ancient town of Pegu (now part of

Myanmar Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...

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

Northern Territory The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, 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 generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

ose rocks of the

Zillertal The Ziller Valley () 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 () and lends its name to the Zillertal Alps, the strongly Glacier, glaciated sectio ...

, in

Tyrol Tyrol ( ; historically the Tyrole; ; ) is a historical region in the Alps of Northern Italy and western Austria. The area was historically the core of the County of Tyrol, part of the Holy Roman Empire, Austrian Empire and Austria-Hungary, f ...

, 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 (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

there are many localities which yield almandine. Fine crystals of almandine embedded in

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

-schist occur near Wrangell in

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

. The coarse varieties of almandine are often crushed for use as an abrasive agent.

Cultural significance

Connecticut Connecticut ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the south. ...

has designated almandine garnet as its state gemstone.

References

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

Occurrence

Cultural significance

See also

References