Brazilianite

Chemistry: Hydrous sodium aluminum phosphate.
Crystal system: Monoclinic; short prism; large spear-shaped.
Color: Transparent to translucent; colorless with striations; yellow/green, yellow, colorless (rare).
Hardness: 5.5
Cleavage: Perfect: 1 direction, parallel to pinacoid faces; Fracture: brittle, conchoidal.
Specific gravity: 2.98
Refractive index: 1.603 – 1.623; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak (merely a change in shade).
Occurrence: Hydrothermal in pegmatite cavities. Brazil, U.S.A.

Notes
Collector's stone; heat sensitive; first found in 1944; may look like beryl, chrysoberyl, topaz, but R.I and DR different.