Beryllonite Explained

Beryllonite
Category:Phosphate minerals
Formula:NaBePO4
Imasymbol:Bel[1]
Strunz:8.AA.10
Dana:38.01.05.01
System:Monoclinic
Class:Prismatic (2/m)
(same H-M symbol)
Symmetry:P21/n
Color:Colorless, white to pale yellow
Habit:Crystals tabular to short prismatic also in spherical aggregates, fibrous, massive; orthorhombic pseudo-symmetry
Twinning:polysynthetic, contact and penetration twins; pseudo-hexagonal stellate forms
Cleavage: perfect; good, interrupted; indistinct; in traces
Fracture:Conchoidal
Tenacity:Brittle
Mohs:5.5 – 6
Luster:Vitreous to adamantine, may be pearly on
Streak:White
Diaphaneity:Transparent to translucent
Gravity:2.8
Opticalprop:Biaxial (−)
Refractive:nα = 1.552 nβ = 1.558 nγ = 1.561
Birefringence:δ = 0.009
2V:68°
References:[2] [3] [4]

Beryllonite is a rare 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.

References

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Notes and References

  1. Warr. L.N.. 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 85. 3. 291–320. 10.1180/mgm.2021.43. 2021MinM...85..291W. 235729616. free.
  2. http://rruff.geo.arizona.edu/doclib/hom/beryllonite.pdf Handbook of Mineralogy
  3. http://www.mindat.org/min-644.html Mindat.org
  4. http://www.webmineral.com/data/Beryllonite.shtml Webmineral data