Dumortierite Value, Price, and Jewelry Information

DUMORTIERITE: Nevada (~2 inches across); Ogilby, California (~1 inch across). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Dumortierite

Dumortierite is a beautiful and very hard material, eminently suitable for jewelry. The cabochon material is the only generally known form, since faceted stones are so rare. Fibrous inclusions have been noted in the transparent Brazilian stones.

Dumortierite Information

Data Value
Name Dumortierite
Varieties Holtite
Alternate Common Names Holtite
Colors Blue, violet, brown, pinkish, blue-green, greenish.
Hardness 8 - 8.5; massive varieties 7.
Fracture Splintery or uneven
Cleavage Good 1 direction, not observed in massive material
Stone Sizes Massive blue and violet material occurs in pieces weighing several pounds. Only a small amount of facetable material has ever been discovered (Brazil, Sri Lanka), and these gems tend to be very small (under 1-2 carats). Only a few faceted dumortierites exist. Arizona dumortierite is actually a quartz-impregnated variety.
Formula Ab7O3(BO3)(SiO4)3.
Crystallography Orthorhombic. Crystals prismatic and very rare; usually massive, fibrous, granular.
Refractive Index 1.668-1.723
Birefringence 0.15-0.37
Luminescence Blue (France) in SW; also blue-white to violet (California) in SW.
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Short
Absorption Spectrum Not diagnostic.
Pleochroism Black/brown/red-brown; also: blue-black/blue/colorless.
Optics a = 1.686; β = 1.722; γ = 1.723. (Brazilian material: a = 1.668-1.673; β = 1.682-1.684; γ = 1.685-1.688). Uniaxial (-), 2V= 13-56°.
Optic Sign Uniaxial -
Luster Vitreous to dull.
Specific Gravity 3.26-3.41
Transparency Transparent to opaque.

See also: Holtite.

Opticsa = 1.686; β = 1.722;γ = 1.723.

Brazil:  a = 1.668-1.673; β= 1.682-1.684; γ= 1.685-1.688. SG = 3.31-3.35.

Uniaxial (-), 2V= 13-56°.

Occurrence: In aluminous metamorphic rocks; in pegmatites.

Pershing County, Nevada: violet gem material. Arizona.

France; Madagascar; Brazil (Minas Gerais): facetable bluish-green material.

Sri Lanka: transparent, reddish-brown stones.

Comments: Dumortierite is a beautiful and very hard material, eminently suitable for jewelry. The cabochon material is the only generally known form, since faceted stones are so rare. Fibrous inclusions have been noted in the transparent Brazilian stones.

Name: After M. Eugene Dumortier, a paleontologist.

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