Silicate of magnesium, iron, and aluminium, belonging to the garnet family. It is more correctly -a group of minerals consisting of mixtures in variable proportions of the two end-members (the theoretical extremes are rarely if ever found in nature). Mixtures in which magnesium clearly predominates over iron are called pyrope; those in which iron predominates are called almandine.
The name garnet, now applied to the entire family, was originally given to the garnets of the pyrope-almandine series, due to their resemblance to red pomegranate seeds (Latin name, malum granatum).
Crystal system Cubic.
Appearance Usually in isolated, granular crystals, often in the form of a perfect rhombic dodecahedron. The color is often reddish brown, but can be a definite red, light red. violet red, or deep blackish red. The crystals, which are often semiopaque, can be transparent and limpid, with highly lustrous faces. They have no cleavage.
Physical properties The hardness is 7 or 7.5 (the higher figure refers to almandine). The density ranges from 3.65-3.87 g/cma for pyrope, to 3.95-4..20 g/cm3 for almandine. Likewise, the refractive index of about 1.730-1.751 for pyrope gradually increases, parallel to the density, to 1.76-1.83 for almandine.
Genesis Pyrope is normally found in peridotitic and eclogitic rocks and also in diamond-bearing kimberlite. Almandine is a characteristic mineral of metamorphic rocks. Due to their resistance to weathering, pyrope and almandine are often found in alluvial, secondary deposits or arenaceous rocks.
Occurrence This mineral is very widespread. Countries famous for garnets usable as gems include Czechoslovakia (Bohemia), South Africa, Madagascar, the United States, Mexico, Brazil, Australia, Burma, Sri Lanka, and India.
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