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 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 Value

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Dumortierite Information

DataValue
NameDumortierite
Alternate Common NamesHoltite
Crystallography Orthorhombic. Crystals prismatic and very rare; usually massive, fibrous, granular.
Colors Blue, violet, brown, pinkish, blue-green, greenish.
Luster Vitreous to dull.
Fracture Splintery or uneven.
Hardness 8-8.5; massive varieties 7.
Specific Gravity 3.26-3.41
Birefringence 0.15-0.37
Cleavage Good 1 direction, not observed in massive material.
Stone SizesMassive 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.
Luminescence Blue (France) in SW; also blue-white to violet (California) in SW.
Spectral Not diagnostic.
FormulaAb7O3(BO3)(SiO4)3.
Pleochroism Black/brown/redbrown; also: blue-black/ blue/colorless.

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.