Demantoid
Variety of andradite
Very Rare · Ca₃Fe³⁺₂(SiO₄)₃
Green andradite garnet with the highest dispersion of any garnet, 0.057 against 0.044 for diamond. Its horsetail inclusions of chrysotile fibres are the mark of the Ural stones, though they also occur in demantoid from Italy and Pakistan. Named for its diamond-like fire.
Identity
- Formula
- Ca₃Fe³⁺₂(SiO₄)₃
- Chemical class
- Silicate
- Mineral group
- Garnet, Grossular, Spessartine, Tsavorite, Uvarovite
- Also known as
- Green andradite garnet
Crystallography
- Crystal system
- Cubic
- Habits
- Dodecahedral, Massive
- Fracture
- Conchoidal
Physical properties
- Mohs hardness
- 6.5
- Density
- 3.84 g/cm³
- Luster
- Adamantine, Vitreous
- Colors
- green, yellow-green, olive green
- Streak
- white
- Transparency
- Transparent
Geology
- Origins
- Metamorphic
- Host rocks
- Ultramafic rock (peridotite, serpentinite), Schist and gneiss
- Associated minerals
- Serpentine, Calcite, Chlorite
- Geography
- Russia (Ural Mountains), Namibia, Iran, Italy
Classification
- Rarity
- Very Rare
- Gem quality
- Yes
Sources
- Demantoid. Mindat.org (Hudson Institute of Mineralogy).
- Demantoid. Gemdat.org (Hudson Institute of Mineralogy).
- J. W. Anthony, R. A. Bideaux, K. W. Bladh, M. C. Nichols, Andradite. Mineral Data Publishing, Handbook of Mineralogy, 2001.
- Andradite. Mindat.org (Hudson Institute of Mineralogy).
- What's the difference between the two green garnets: tsavorite and demantoid?. Gemological Institute of America.
- U. Hennebois, A. Delaunay, S. Karampelas, E. Fritsch, Faceted Demantoid Garnet with Spectacular "Horsetail" Inclusions. Gems & Gemology, Micro-World, Winter 2021, Gemological Institute of America, 2021.
- Andradite. Wikipédia, l'encyclopédie libre (fr).
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