Beryllonite

Beryllonite
Beryllonite (whitish) with tourmaline variety indicolite (blue) from Paprok, Nuristan Province, Afghanistan. Specimen size 4 cm
General
Category	Phosphate minerals
Formula (repeating unit)	NaBePO4
Strunz classification	8.AA.10
Dana classification	38.01.05.01
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/n
Identification
Color	Colorless, white to pale yellow
Crystal habit	Crystals tabular {010} to short prismatic also in spherical aggregates, fibrous, massive; orthorhombic pseudo-symmetry
Twinning	polysynthetic, contact and penetration twins; pseudo-hexagonal stellate forms
Cleavage	{010} perfect; {100} good, interrupted; {101} indistinct; {001} in traces
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	5.5 - 6
Luster	Vitreous to adamantine, may be pearly on {010}
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.8
Optical properties	Biaxial (-)
Refractive index	nα = 1.552 nβ = 1.558 nγ = 1.561
Birefringence	δ = 0.009
2V angle	68°
References

Beryllonite is a rare sodium beryllium phosphate mineral with formula NaBePO₄. The tabular to prismatic monoclinic crystals vary from colorless to white or pale yellowish, and are transparent with a vitreous luster. Twinning is common and occurs in several forms. It exhibits perfect cleavage in one direction. The hardness is 5.5 to 6 and the specific gravity is 2.8. Refractive indices are nα = 1.552, nβ = 1.558 and nγ = 1.561. A few crystals have been cut and faceted, but, as the refractive index is no higher than that of quartz, they do not make very brilliant gemstones.

It occurs as a secondary beryllium mineral in granitic and alkalic pegmatites. It was first described from complex crystals and as broken fragments in the disintegrated material of a granitic vein at Stoneham, Oxford County, Maine where it is associated with feldspar, smoky quartz, beryl and columbite. It was discovered by James Dwight Dana in 1888, and named beryllonite for its beryllium content.