Greifensteinite

Greifensteinite
240px Greifensteinite (picture size: 3 mm)
General
Category	Phosphate mineral Roscherite group
Formula (repeating unit)	Ca2Fe2+5Be4(PO4)6(OH)4·6H2O
Strunz classification	8.DA.10
Dana classification	42.7.7.4
Crystal symmetry	Monoclinic prismatic H-M symbol: (2/m) Space group: C 2/c
Unit cell	a = 15.903 Å, b=11.885 Å, c=6.677 Å; β=94.68; Z=2
Identification
Color	Yellow green, olive green, light brown
Crystal habit	Prismatic
Crystal system	Monoclinic
Cleavage	Good on {100} (or parting on {100})
Fracture	Uneven
Tenacity	brittle
Mohs scale hardness	4.5
Luster	Vitreous
Streak	White, greenish
Diaphaneity	Transparent to translucent
Specific gravity	2.93
Optical properties	Biaxial (-)
Refractive index	nα: 1.624 nβ: 1.634 nγ: 1.638
Birefringence	0.014
2V angle	80°
References

Greifensteinite is beryllium phosphate mineral with formula: Ca₂Fe²⁺₅Be₄(PO₄)₆(OH)₄·6H₂O. It is the Fe²⁺ dominant member of the roscherite group. It crystallizes in the monoclinic crystal system and typically forms prismatic dark olive green crystals.

It was first described in Germany at Greifenstein Rocks, Ehrenfriedersdorf, and was named for the location. At the type locality it occurs within a lithium-rich pegmatite in miarolitic cavities. It was approved by the International Mineralogical Association in 2002.

References

• Rastsvetaeva R K, Gurbanova O A, Chukanov N V (2006) Crystal structure of greifensteinite Ca₂Fe²⁺☐Mg₂Fe²⁺₂Be₄(PO₄)₆(OH)₄·6H₂O. Doklady Chemistry 41, 18-25 [1]