Almandine

 ( Garnet Gemstones ) 

Almandine (), also known as almandite, is a 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, a town in Caria in Asia Minor. Almandine is an iron aluminum garnet, of deep red color, inclining to purple. It is frequently cut with a convex face, or en cabochon, and is then known as carbuncle. Viewed through the spectroscope in a strong light, it generally shows three characteristic .

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: Fe₃Al₂(SiO₄)₃. Magnesium substitutes for the iron 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 Silicate mineral, which are the main constituents of the Earth's crust, upper mantle and transition zone. Almandine crystallizes in the cubic space group Iad, with unit-cell parameter a ≈ 11.512 Å at 100 K.

Almandine is with the Néel temperature of 7.5 K. It contains two equivalent magnetic sublattices.

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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 Thanlyin, an ancient town of Pegu (now part of Burma). 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 occur in the rocks of the Zillertal, in Tyrol, and are sometimes cut and polished. An almandine in which the ferrous oxide is replaced partly by Magnesium oxide 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. The coarse varieties of almandine are often crushed for use as an abrasive agent.

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Cultural significance Connecticut has designated almandine garnet as its state gemstone.

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See also

• List of minerals

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