Vesuvianite

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Vesuvianite

General Category

Sorosilicate

Formula

(repeating unit) Ca10(Mg, Fe)2Al4(SiO4)5(Si2O7)2(OH,F)4

IMA symbol Ves[1]

Strunz classification 9.BG.35

Crystal system Tetragonal

Crystal class Ditetragonal dipyramidal (4/mmm)

H-M symbol: (4/m 2/m 2/m)

Space group P4/nnc

Unit cell a = 15.52 Å, c = 11.82 Å

Z = 2

Identification

Color Yellow, green, brown; colorless to white, brown-black, light green, emerald green, violet, blue-green to blue, pink, purple, red, black, commonly zoned

Crystal habit Short pyramidal to long prismatic crystals common, massive to columnar

Twinning Fine twin domains observed

Cleavage Poor on {110} and {100} very poor on {001}

Fracture Sub conchoidal to irregular

Tenacity Brittle

Mohs scale hardness 6–7

Luster Vitreous to resinous

Streak White

Diaphaneity Subtransparent to translucent

Specific gravity 3.32–3.43

Optical properties Uniaxial (−)

Refractive index nω = 1.703–1.752

nε = 1.700–1.746

Birefringence 0.004–0.006

Pleochroism slight in colored varieties

Solubility Vesuvianite is virtually insoluble in acids

Other characteristics striated lengthwise

References [2][3][4]

Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism.[3] It was first discovered within included blocks or adjacent to lavas on Mount Vesuvius, hence its name. Attractive-looking crystals are sometimes cut as gemstones. Localities which have yielded fine crystallized specimens include Mount Vesuvius and the Ala Valley near Turin, Piedmont.[5]

The specific gravity is 3.4 and the Mohs hardness is 6+1⁄2. The name "vesuvianite" was given by Abraham Gottlob Werner in 1795, because fine crystals of the mineral are found at Vesuvius; these are brown in color and occur in the ejected limestone blocks of Monte Somma. Several other names were applied to this species, one of which, "idocrase" by René Just Haüy in 1796, is now in common use.[5]

A sky bluish variety known as cyprine has been reported from Franklin, New Jersey and other locations; the blue is due to impurities of copper in a complex calcium aluminum sorosilicate. Californite is a name sometimes used for jade-like vesuvianite, also known as California jade, American jade or Vesuvianite jade. Xanthite is a manganese rich variety. Wiluite is an optically positive variety from Wilui, Siberia. Idocrase is an older synonym sometimes used for gemstone-quality vesuvianite.