Garnet Group: Almandine Garnet (Ceylon-Ruby)
Almandine & Rhodolite Garnet used in Jewelry
Source: Australia, Burma, East Africa, Sri Lanka, USA (Alaska, New York)
The name "almandine" was derived from alabandicus; a name coined by Pliny the Elder [3] to lesser carbuncle gemstones discovered at Alabanda, in Asia Minor. Almandine garnet is sometimes mistakenly referred to as "almandite."
Almandine belongs to the "garnet group" of minerals commonly found within metamorphic rock and associated with ultramafic igneous rock formations. Garnet is classified as a nesosilicate in the Silicate mineral group. There are six common varieties of garnet that are identified by their chemical composition and color. They are almandine, andradite, grossularite (tsavorite), pyrope, spessartite, and uvarovite.
Almandine is an iron alumina (iron aluminum silicate) garnet variety, and when the iron is substituted with magnesium it becomes the magnesium aluminum garnet, pyrope. Almandine is commonly found embedded in, or associated with mica-schist or gneiss.
Almandine in Gneissic Matrix - Eurico Zimbres |
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Needle Inclusions in Almandine - © AGS Labs |
The color of almandine garnet tends to be redish-orange, reddish brown, brownish-red, deep-red, or purplish-red. Purplish-violet varieties are sometimes referred to as "Syriam garnet," or "Pegu garnet," named after Syriam, a capital of the ancient kingdom of Pegu (Bago), in Lower Burma. Syriam garnet may also be referred to as "amethystine or oriental garnet.
Rhodolite (Ceylon-Ruby)
Often referred to as "Ceylon-ruby" the rose-pink to ruby-red gem variety of pyrope-almandine garnet is known as "rhodolite," derived from the Greek words rhodon lithos, or "rose-like stone."
Rhodolite is a combination of almandite and pyrope garnet, containing trace amounts of aluminum (Al), Iron (Fe) and magnesium (Mg) as allochromatic coloring agents. Primary sources for Rhodolite are found in Kenya, Mozambique, Sri Lanka (Ceylon), the United States, and Zimbabwe.
When significant deposits of gem-quality almandine were discovered in South Australia's Northern Territory, they were nicknamed "Australian rubies." Almandine has also been discovered near Fort Wrangell, Alaska.
Like other members of the garnet group, almandine forms rounded crystals with 12 rhombic, or 24 trapezoidal faces. Almandine is single refractive, and may exhibit anomalous double refraction when viewed with a polariscope [4]. When viewed through a spectroscope under a strong lighting, almandine can exhibit three characteristic absorption bands.
Almandine Garnet Crystallography, Chemistry, Physical Properties
Almandine Garnet Optical Properties
Bibliography on Garnet Gemstones
1. Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy  . Gemstone Press
2. Judith Crowe, The Jeweler's Directory of Gemstones . DK Publishing.
3. Gem Diamond Foundation, Alabandicus, Almandine, Garnet . www.farlang.com
4. Charles Lewton-Brain, Polariscopes for Gemology . www.ganoksin.com
5. 1902 Encyclopedia, Garnet . www.1902encyclopedia.com
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