Nabalamprophyllite

Nabalamprophyllite
General
Category	Sorosilicate
Formula; (repeating unit)	Ba(Na,Ba){Na3Ti[Ti2O2Si4O14](OH,F)2}
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) ; (same H-M symbol)
Space group	P2/m
Unit cell	a = 19.805, b = 7.123 ; c = 5.426 [Å]; β = 96.45; Z = 2 ; V = 753.4 Å3
Identification
Color	Brown to bright yellow crystals
Crystal habit	Prismatic, sheaf-like, random aggregates
Cleavage	Perfect (001)
Mohs scale hardness	3
Luster	Glassy
Streak	White
Diaphaneity	Transparent to translucent
Optical properties	Biaxial positive
Refractive index	nα=1.750, nγ=1.799
Pleochroism	Weak, green-brown
2V angle	40.5°
References	[1][2]

Nabalamprophyllite has a general formula of Ba(Na,Ba){Na₃Ti[Ti₂O₂Si₄O₁₄](OH,F)₂}.[2] The name is given for its composition (Naba, meaning sodium, Na and barium, Ba) and relation to other lamprophyllite-group minerals. Lamprophyllite is a rare Ti-bearing silicate mineral usually found in intrusive igneous rocks.[3]

Nabalamprophyllite is monoclinic, which means crystallographically, it contains three axes of unequal length and the angles between two of the axes are 90°, and one is less than 90°. It belongs to the space group P2/m.[2] The mineral also has an orthorhombic polytype (nabalamprophyllite-2O).[4] This mineral belongs to the space group Pnmn. In terms of its optical properties, nabalamprophyllite is anisotropic which means the velocity of light varies depending on direction through the mineral. Its calculated relief is 1.86 - 1.87.[1] Its color in plane polarized light is green-brown, and it is weakly pleochroic.

The mineral has only been found in Russia, usually in association with coarse-grained igneous rocks called pegmatites. The type localities are the Inagli alkaline–ultrabasic massif, Yakutia and the Kovdor alkaline–ultrabasic massif in the Kola Peninsula.

References

Webmineral data
Philonen, P.C., Grew, E.S., Ercit, T.S., Roberts, A.C., Jambor, J.L. (2005) New mineral names. American Mineralogist, 90, 1227-1233
Klein, C., Dutrow, B. (2007) The 23rd edition of the Manual of Mineral Science. John Wiley Publishers, p.497.
Sokolova, E., Hawthorne, F.C. (2008) From Structure Topology to Chemical Composition. IV. Titanium Silicates: The Orthorhombic Polytype of Nabalamprophyllite from the Lovozero Massif, Kola Peninsula, Russia. The Canadian Mineralogist, 46, 1323-1331.

N.V. Chukanov, M.M. Moiseev, I.V. Pekov, K.A. Lazebnik, R.K. Rastsvetaeva, N.V. Zayakina, G. Ferraris, G. Ivaldi (2004) Nabalamprophyllite Ba(Na,Ba){Na₃Ti[Ti₂O₂Si₄O₁₄](OH,F)₂}, a new layer titanosilicate of the lamprophyllite group from the Inagli and Kovdor alkaline-ultrabasic massifs, Russia. Zapiski Vseross. Mineral. Obshch., 133(1), 59–72 (in Russian, English abstract).

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[Webmin-1] Webmineral data

[Philonen-2] Philonen, P.C., Grew, E.S., Ercit, T.S., Roberts, A.C., Jambor, J.L. (2005) New mineral names. American Mineralogist, 90, 1227-1233

[3] Klein, C., Dutrow, B. (2007) The 23rd edition of the Manual of Mineral Science. John Wiley Publishers, p.497.

[4] Sokolova, E., Hawthorne, F.C. (2008) From Structure Topology to Chemical Composition. IV. Titanium Silicates: The Orthorhombic Polytype of Nabalamprophyllite from the Lovozero Massif, Kola Peninsula, Russia. The Canadian Mineralogist, 46, 1323-1331.