The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Orthorhombic; crystals prismatic, chunky, with etched surfaces and striations.|
|Colors||Colorless to greenish white; may be stained yellow. Streak: white.|
|Luster||Vitreous to greasy.|
|Cleavage||None; fracture conchoidal; brittle.|
|Stone Sizes||This is an extremely rare mineral, and small clean cuttable fragments have yielded minute faceted stones. They are transparent and colorless, all under 1 carat in size.|
Optics: a = 1.595; β= 1.601; γ= 1.604.
Occurrence: In pegmatite with muscovite, albite, and other minerals at the Smith Mine, Chandlers Mill, Newport, New Hampshire.
Name: After Cornelius Hurlbut, well-known professor of mineralogy at Harvard University.