This paper presents data on burovaite-Ca, the first Ti-dominant member of the labuntsovite group with a calcium D-octahedron.
The idealized formula of burovaite-Ca is (K,Na)
4Ca
2(Ti,Nb)
8[Si
4O
12]
4(OH,O)
8 · 12H
2O. The mineral has been found in the hydrothermal zone of aegirine-microcline pegmatite located in khibinite at Mt. Khibinpakhkchorr,
the Khibiny pluton, Kola Peninsula, Russia. Radiaxial intergrowths of burovaite-Ca and labuntsovite-Mn associated with lemmleynite-Ba,
analcime, and apophyllite have been identified in caverns within microcline. The mean composition of the mineral is as follows,
wt %: 3.72 Na
2O, 2.76 K
2O, 4.22 CaO, 0.47 SrO, 0.23 BaO, 0.01 MnO, 0.30 Fe
2O
3, 0.14 Al
2O
3, 42.02 SiO
2, 17.30 TiO
2, 15.21 Nb
2O
5, 12.60 H
2O (measured); the total is 98.98. Its empirical formula has been calculated on the basis of [(Si,Al)
16O
48]: {(Na
3.10K
1.07Ca
0.37Sr
0.04Ba
0.04)
4.62}(Ca
1.28Zn
0.01)
1.29(Ti
4.97Nb
2.56Fe
0.08Ta
0.02)
7.63(Si
15.93Al
0.07)
16O
48(OH
6.70O
0.93)
7.63 · 12H
2O. The strongest lines in the X-ray powder diffraction pattern of burovaite-Ca (
I-d Å] are as follows: 70–7.08, 40–6.39, 40–4.97, 30–3.92, 40–3.57, 100–3.25, 70–3.11, 50–2.61, 70–2.49, 40–2.15, 50–2.05, 70–1.712,
70–1.577, and 70–1.444. The structure of burovaite-Ca was solved by A.A. Zolotarev, Jr. The mineral is monoclinic, space group
C2/
m. The unit-cell dimensions are
a = 14.529(3),
b = 14.203(3),
c = 7.899(1), β = 117.37(1)°,
V = 1447.57 Å
3. Burovaite-Ca is an isostructural Ti-dominant analogue of karupmøllerite-Ca and gjerdingenite-Ca. Two stages of mineral formation—pegmatite
proper and hydrothermal—have been recognized in the host pegmatite. The hydrothermal stage included K-Ba-Na, Na-K-Ca, and
Na-Sr substages. Burovaite-Ca is related to the intermediate Na-K-Ca substage. At the first substage, labuntsovite-Mn and
lemmleynite-Ba were formed, and tsepinite-Na, paratsepinite-Nd, and tsepinite-Sr were formed at the final substage. Thus,
the sequence of crystallization of labuntsovite-group minerals is characterized by the replacement of the potassium regime
by the sodium regime of alkaline solutions in the evolved host pegmatite.
Original Russian Text © Yu.V. Azarova, Z.V. Shlyukova, A.A. Zolotarev, Jr., N.I. Organova, 2009, published in Zapiski RMO
(Proceedings of the Russian Mineralogical Society), 2009, Pt. CXXXVII, No. 2, pp. 40–52.
The mineral and its name considered by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, December
15, 2007. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, March 31,
2008.