Almandine is perhaps the most common garnet. Gemstones always have some spessartine and pyrope components, and this creates a wide range of colors, including brown, red-brown, purplish red, wine red, purple, and deep red. Inclusions of asbestiform minerals (pyroxene or amphibole) create a chatoyancy that yields, in cabochons, a 4-rayed star.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Garnet|
|Refractive Index||1.75 – 1.83|
|Hardness||7 – 7.5|
|Specific Gravity||3.95 - 4.30|
|Density||3.95 - 4.3|
|Spectral||The spectrum of almandine is distinctive and diagnostic: there is a band 200 Å wide at 5760 (strong) and also strong bands at 5260 and 5050. Lines may appear at 6170 and 4260. This pattern of 3 (or sometimes 5) bands is seen in all almandines, and most garnets with a significant almandine component.|
Almandine is perhaps the most common garnet. Gemstones always have some spessartine and pyrope components, and this creates a wide range of colors, including brown, red-brown, purplish red, wine red, purple, and deep red. Inclusions of asbestiform minerals (pyroxene or amphibole) create a chatoyancy that yields, in cabochons, a 4-rayed star. Star gems come primarily from Idaho and India. The Idaho material has N= 1.80X, density 4.07 (up to 4.76 due to inclusions). Inclusions in faceted gems vary widely, but are usually not too obtrusive. This is especially true of the silk, which is often visible only under magnification.
One of the classic sources of this garnet is Alabanda, in Asia Minor. Its common name is a modification of the source. The Roman historian Pliny wrote of them.
Almandine is a widespread constituent of metamorphic rocks; also in igneous rocks, in contact metamorphic zones, and as an alluvial mineral.
OPTICS: N= 1.75-1.83; usually above 1.78.
INCLUSIONS: Almandine is usually included with a variety of minerals. There are zircon crystals with haloes due to radioactivity; irregular, dotlike crystals, and lumpy crystals; futile needles, usually short fibers, crossed at 110° and 70°; there are dense hornblende rods (especially from Sri Lanka); asbestiform needles of augite or hornblende that run parallel to the dodecahedral edges; also apatite; ilmenite; spinet; monazite: biotite; quartz.
Colorado; South Dakota; Michigan; New York; Pennsvlvania; Connecticut; Maine.
Canada; Uruguay; Greenland; Norway; Sweden; Austria; Japan; Tanzania; Zambia.
Fort Wrangell, Alaska: fine, well-formed crystals in slate.
California; Idaho: star garnets.
Major gem almandine sources are as follows:
India: Jaipur (in mica schist); also Rajasthan and Hyderabad; some stars also.
Sri Lanka: at Trincomalee, fine color and large size.
Brazil: Minas Cerais; Bahia.
Idaho: star garnets.
Madagascar: large sizes.
Our common, dark red garnets are a blend of almandine and pyrope. Throughout history, this has been one of the most popular gems. They are found world wide and in great abundance. Hence, the value is low.
Very large crystals exist, but because of their dark tone, only small to medium sized gems are faceted. These are cut very shallow, to let light pass through.
Almandine garnets from Idaho and India sometimes have asbestos fiber inclusions. These will produce star stones when properly cut. They are highly prized by collectors, because of their rarity. They are also one of the most difficult gems to cut.
Almandines of large size are known, such as the 60-cm crystals in rock at the Barton Mine, New York. This material is so badly shattered that stones up to only 1-2 carats can be cut from the fragments. Indian and Brazilian almandine constitutes the bulk of material on the marketplace.
Smithsonian Institution (Washington, D.C): 174 and 67.3 (stars, red-brown, Idaho); 40.6 (red-brown, Madagascar).