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Chemical composition Complex calcium aluminum silicate
Crystal system Tetragonal
Habit Prismatic terminated by truncated pyramids, massive, fibrous
Cleavage Poor
Fracture Sub-conchoidal
Hardness 6.5
Optic nature Uniaxial +/-
Refractive index 1.700 - 1.725
Birefringence 0.005
Dispersion Low, 0.019
Specific gravity 3.25-3.50
Lustre Vitreous
Pleochroism Weak to distinct (shades of body color)
Faceted idocrase

Idocrase image gallery

Synonyms: Vesuvianite, Ambosselite
Idocrase was first discovered on Mount Vesuvius and originally named vesuvianite in 1795 by the famous mineralogist Abraham Gottlob Werner . The French mineralogist Rene Just Hauy suggested it should be named Idocrase four years later. Both names are used interchangeably. The Gemological Institute of America prefers idocrase.

Variental Names: Cyprine, Californite

Cyprine is a blue copper containing variety of idocrase (vesuvianite) that was first described from Norway about 1821 by the famous mineralogist Berzelius; the name is derived from Cyprium, the ancient term for copper.

Californite is a compact massive form of idocrase that has an appearance to poor quality jade. It has historically be used as a jade simulant.

Crystal System

Tetragonal or monoclinic

Crystal Habit

Prismatic to equant stubby crystals; massive granular to fine grained.

Chemical composition

Ca19(Al,Mg)13B0-5(Si2O7)4(SiO4)10(O,OH,F)10 often containing trace to minor amounts of iron, copper up to 2.1% (as Cu in cyprine), chromium, manganese, titanium, boron or beryllium.


Recently, idocrase has been misrepresented and sold as transparent hydrogrossular garnet. It's properties can be essentially indistinguishable from hydrogrossular garnet with standard gem testing equipment.

Peridot has a lower refractive index (1.654 to 1.670).The californite variety of vesuvianite (idocrase) floats or sinks slowly in methylene iodide; jadeite sinks (specific gravity less than 3.3). Nephrite has a lower specific gravity (3.295).

===Color=== yellow, yellowish green, green, emerald green, yellow brown, brown, blue, violet to magneta; sometimes displays distinct color zoning.


Idocrase often shows a "heat-wave" effect similar to grossular garnet.
Under magnification, the cyprine variety may exhibit a distinctly fibrous appearance.

===Cleavage=== poor on {110}, {100} and very poor on {001}

===Specific Gravity=== 3.32 - 3.34 (measured); 3.42 (calculated)

Optical Nature

Uniaxial (+) or Uniaxial (-); biaxial idocrase has been observed. Idocrase appearing singly refractive has been observed.

Refractive Index

nω = 1.703 – 1.752 nε = 1.700 – 1.746. The variety cyprine from Franklin New Jersey demonstrates a lower range of refractive indices, with nω = 1.696 – 1.712 nε = 1.710 – 1.719.

Birefringence: approximately 0.005; it can be so extremely low (0.001), that it is often indistinguisable with standard refractometers.

The optical character of idocrase is uniaxial with mostly a negative optic sign. Hydroxyl rich gemstones may be uniaxial +.
Sometimes idocrase can be isotropic or biaxial +, in some zoned crystals the optic nature can be biaxial in some areas and uniaxial in other.


Weak; nω = colorless to yellowish, nε = yellowish, greenish, brownish


Spectrum of idocrase: absorption band at 464nm.


None known


None known


None known


None known


See Vesuvianite


  • Deer, Howie & Zussman: An Introduction to Rock Forming Minerals
  • Anthony, John W., Bideaux, Richard A., Bladh, Kenneth W., and Nichols, Monte C. (1990): Handbook of Mineralogy: Mineral Data Publishing, Tucson, Arizona
  • Kunz, George Frederick (1903), American Journal of Science, 4th. Series, Vol. 16 pp397-398 “Californite (vesuvianite); a new ornamental stone”
  • Palache, Charles, Harry Berman & Clifford Frondel (1944): The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Seventh edition
  • Shannon, E. V. (1922) Note on the cyprine from Franklin Furnace, New Jersey. American Mineralogist, 7, 140-142.
  • Introduction to Optical mineralogy (2004) - William D. Nesse ISBN 0195149106