Danburite

Chemistry: Calcium boro-silicate
Crystal system: Orthorhombic; striated prisms of diamond-shaped cross section, terminated by domes; distinctive chisel-shape appearance; habits similar to topaz.
Color: Transparent; yellow and colorless; rarely pink.
Hardness: 7
Cleavage: None; Fracture: sub-conchoidal.
Specific gravity: 3.0
Refractive index: 1.63 – 1.64; Biaxial positive/negative; 0.006
Luster: Vitreous.
Dispersion: Low
Dichroism: -
Occurrence: Burma, Madagascar, Mexico, Australia.

Notes
Collector’s stone; distinguished from topaz (S.G = 3.53) by lower S.G; Apatite (D.R: 0.003) by higher D.R and Tourmaline (D.R: 0.018) by lower D.R; may show rare earth spectrum; usually faceted.