Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Demantoid was discovered in Russia in the early 19th century. In 1854, the noted mineralogist Nils Gustaf Nordenskiöld identified this gem as a variety of andradite garnet.
As a rare gem variety, demontoid garnet is highly prized by both gem collectors and jewelry enthusiasts. The chemical formula is Ca3Fe2(SiO4)3 with chromium substitution as the cause of the demantoid green color. Ferric iron is the cause of the yellow in the stone.
Some stones have a diamond-like fire and are also found in emerald green colours. Clean, facetable stones command very high prices per carat. The horsetail inclusion of demontoid garnets is very popular among gem collectors. ( wavy, golden, and fibrous ).
Demontoid Garnet can be found in Russia, Namibia, Madagscar, Afghanistan; Azerbaijan; Canada; Democratic Republic of the Congo; Iran; Mexico; Pakistan; South Korea; Sri Lanka; San Benito County, California, United States.
Refractive Index is 1.881-1.888 and can be found in colours yellow-green, green, deep green. Demantoid is red in the Chelsea filter.
• Luster: Adamantine
• Hardness: 6.5-7
• Fracture: Conchoidal
• Specific Gravity: 3.82-3.88
• Birefringence: None
• Cleavage: None
• Dispersion: 0.057
• Heat Sensitivity: Yes
• Enhancements: Heat treatment
• Transparency: Transparent
• Phenomena: Occasional chatoyancy due to fibrous inclusions.
• Birthstone: January
• Formula: Ca3Fe2Si3O12, chromium (Cr) traces cause green color, ferric iron (Fe3+) traces cause yellow color.
• Pleochroism: None.
• Optical Properties: Isotropic ( M/B anomalous birefringence )
• Inclusions: Horsetail inclusions of byssolite (fibrous amphibole) or chrysotile.