Babefphite

Babefphite
General
Category	Phosphate mineral
Formula (repeating unit)	BaBe(PO4)(F,OH)
IMA symbol	Bbf
Strunz classification	8.BA.15
Crystal system	Triclinic
Crystal class	Pedial (1) (same H-M symbol)
Space group	F1
Unit cell	a = 6.889 Å, b = 16.814 Å, c = 6.902 Å; α = 90.01°, β = 89.99°, γ = 90.32°; Z = 8
Identification
Color	White
Crystal habit	As anhedral, equant to flattened grains, to 1.5 mm; may be in aggregates, (pseudotetragonal)
Tenacity	Brittle
Mohs scale hardness	3.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	4.31
Optical properties	Uniaxial (+) – biaxial positive (pseudouniaxial)
Refractive index	nω = 1.629 nε = 1.632
Birefringence	0.003
References

Babefphite is a rare phosphate mineral with the general formula BaBe(PO₄)(F,OH). The name is given for its composition (Ba meaning barium, Be meaning beryllium, F meaning fluorine, and P for phosphorus).

Crystallography

Babefphite is tetragonal, which means crystallographically, it contains two horizontal and interchangeable equal axes (a_{1 and 2}) and a longitudinal axis (c). It belongs to the 4/m 2/m 2/m point group; meaning it has four horizontal axes of twofold symmetry, two of which coincide with the crystallographic axes (a₁) and (a₂) and the remaining two at 45° to the (a₁) and (a₂).

Optical properties

Babefphite is an anisotropic mineral meaning that the velocity of light passing through it will vary depending on the direction of travel. When measured against Canada Balsam it will display moderate positive relief. Relief is an optical property that relates the index of refraction of a mineral versus the index of refraction of another material. Positive relief denotes light being bent toward the mineral. Negative relief means the light is bent toward the mounting material. In the case of optical mineralogy, this other material is most often whatever material is used to mount the mineral in question in thin section. Based on the white color of babefphite in hand sample it is likely that it appears clear in thin section under plane polarized light. Due to its anisotropic nature, it has the possibility of displaying very weak pleochroism under the same conditions. Pleochroism is defined as a change of color, on rotation, of plane light. It occurs when the extraordinary and ordinary rays of light are absorbed differently, thereby displaying different colors. The wider the difference in the rays the more dramatic the color change. Babefphite is also weakly birefringent. Birefringence is an optical property that is determined by the direction that light passes through a mineral.

Occurrence

Babefphite was first described in 1966 for an occurrence at the Aunik fluorite-rare metals deposit, Buryatia, Eastern-Siberian Region, Russia. It has also been reported from the Rožná pegmatite in the Vysočina Region, Moravia, Czech Republic.

In the Siberian occurrence it occurs in residual material above rare-earth metal bearing skarns associated with alkaline intrusive bodies. It occurs with zircon, ilmenorutile, fluorite, phenakite, scheelite, bertrandite, albite, microcline and quartz.