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www.mineralgallery.co.za Minerals A-E |
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Almandine |
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Name
Almandine
Chemistry
FE3AL2(SIO4)3
Uses
As a gemstone or as an abrasive
Color
Typically red but oftentimes brown
Hardness
6.5-7.5
Specific gravity
4-4.3
Streak
White
Crystals
(Cubic) rhombododecohedral, icositerahedron; intergrowth; and superficial growth; seldom twinning
Accompanied by:
Quartz, feldspars, mica, calcite, chlorite, idocrase, magnetite, chromite and wollastonite
Similar to:
Pyrope, spessartite, ruby, spinel, glass imitations
Almandene belongs to the garnet group.
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The better deeper red colors are oftentimes cut as gemstones. It's close relative is the pyrope. It is denser than the pyrope. The Almandine color is caused by iron combining with the aluminum.
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Typical crystal habit is the 12 or 24 trapezoidal faces of the rounded crystals. The crystals are translucent to transparent. They can be found in schist where they can also be found in massive forms.
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Iron- rich almandine, the most common garnet, is widespread in metamorphic rocks such as schists and gneisses and in granitic igneous rocks.
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The magnesium garnet, favored by high pressures of formation, is found in magnesium-rich m pth and is an important mineral in the mantle of the Earth.
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Spessartine is found in manganese rich gneisses and in coarse-grained, granite like bodies called pegmatites.
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Garnet is commonly cut as a gem. The dark red, Victorian garnet jewelry was made from pyrope garnets mined in Bohemia, now a part of the Czech Republic. Grossular makes hessonite, an attractive, cinnamon brown stone, and demantoid, the green variety of andradite, is rare and highly prized. Synthetic yttrium-aluminum garnet, or YAG, is used to imitate diamond as a gem. Garnet is also used as an abrasive.
