Zircophyllite

Zircophyllite
General
Category	Inosilicate
Formula (repeating unit)	(K,Na)3(Mn,Fe^2+)7(Zr,Ti)2Si8O24(O,OH,F)7
Strunz classification	9.DC.05
Dana classification	69.1.1.5
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Identification
Color	Black-brown
Crystal habit	Platy, micaceous
Cleavage	Perfect on {001}
Fracture	Brittle
Tenacity	Brittle
Mohs scale hardness	4 - 4.5
Luster	Adamantine, vitreous
Streak	Light brown
Diaphaneity	Translucent to opaque
Specific gravity	3.34
Optical properties	Biaxial (-)
Refractive index	nα = 1.708 nβ = 1.738 nγ = 1.747
Birefringence	δ = 0.039
Pleochroism	X = Y = dark yellow; Z = brown
2V angle	Measured: 62°, calculated: 56°
Common impurities	Hf,H2O
References	[1][2][3]

Zircophyllite is a complex mineral, formula (K,Na)₃(Mn,Fe)₇(Zr,Ti,Nb)₂Si₈O₂₄(OH,F)₇. It crystallizes in the triclinic - pinacoidal crystal class as dark brown to black micaceous plates. It has perfect 001 cleavage, a Mohs hardness of 4 to 4.5 and a specific gravity of 3.34. Its indices of refraction are nα=1.708 nβ=1.738 nγ=1.747 and it has a 2V optical angle of 62°.

It occurs with natrolite in alkali pegmatites. It was discovered in 1972 in the Korgeredabinsh massif, Tuva, Russia and is named for its zirconium content and its relationship to astrophyllite. It is also known from the Mont Saint-Hilaire intrusive complex of Québec, Canada.

Zircophyllite is radioactive, but the radioactivity is barely detectable.^[2]

References

1. Mindat.org
2. Webmineral data
3. Handbook of Mineralogy