Brookite is a very dark-colored mineral, transparent only in small fragments. Cuttable crystals are exceedingly rare, and attractive-looking cut stones are among the rarest of all gems. Most stones are in private collections.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Orthorhombic. Occurs only in crystals; tabular, prismatic, pyramidal; often striated.|
|Colors||Brown, yellow brown, reddish brown, dark brown to black; rarely blue.|
|Luster||Adamantine to submetallic.|
|Hardness||5.5 - 6|
|Density||4.14 normal; 3.87 – 4.14|
|Birefringence||0.122 – 0.157|
|Dispersion||Strong, ~ 0.131|
|Stone Sizes||Always less than 1-2 carats; larger stones are opaque.|
|Pleochroism||Strong: yellow-brown/ reddish-brown/ orange to golden brown. An hourglass-shaped zonal coloration is sometimes seen in bluish crystals.|
OPTICS: a = 2.583; β = 2.584; γ = 2.700 – 2.740
OCCURRENCE: In gneisses, schists and sometimes in igneous rocks; contact deposits.
North Carolina; Somerville, Massachusetts; Maine; California.
Magnet Cove, Arkansas: contact metamorphic rocks.
Ellenville, New York: hydrothermal deposits.
Tirol, Switzerland: typical Alpine deposits
Minas Gerais, Brazil: Dartmoor, England; France; USSR.
COMMENTS: Brookite is a very dark-colored mineral, transparent only in small fragments. Cuttable crystals are exceedingly rare, and attractive-looking cut stones are among the rarest of all gems. Most stones are in private collections.
NAME: After the English mineralogists and crystallographer J.H. Brooke.