IMA 2008-001 = burovaite-Ca

[Marco E. Ciriotti]

Il nome di questa nuova specie (IMA 2008-001) del gruppo della labuntsovite [kuzmenkoite subgroup] è stato anticipato da Pavel M. Kartashov in: http://www.mindat.org/gallery.php?loc=13573

La formula è (Na,K)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O.
I dati cristallografici sono i seguenti: mon C2/m 14.529 14.203 7.899 90.00 117.37 90.00 2
La classificazione Strunz & Nickel è: 9 C E 30 c

Il nome è burovaite-Ca (in questo caso il simbolo del calcio non va scritto in parentesi in quanto, come per le zeoliti, anche nelle labuntsoviti, si tratta di cationi extra-framework).

[Marco E. Ciriotti]

Tatyana A. Burova, cui il nuovo minerale è stato dedicato, è una valente mineralogista russa, che insieme a Semenov, per prima studiò le labuntsoviti.

[Marco E. Ciriotti]

La descrizione-tipo della burovaite è ora pubblicata.

Referenza:
• Azarova, Yu.V., Shlyukova, Z.V., Zolotarev, A.A., Jr., Organova, N.I. (2009): Burovaite-Ca, (Na,K)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O-the new labuntzovite group mineral and its position in lowtemperature mineral-forming processes within pegmatites of Khibiny massif, Russia. Proceedings of the Russian Mineralogical Society, 138(2), 40-52.

Abstract:
The paper displays data on the mineral — burovaite-Ca — the first Ti-dominant representative of labuntsovite group with a calcium D-octahedron. Idealized formula of burovaite-Ca — (Na,K)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O. The mineral has been found in hydrothermal zone of aegirine-microcline pegmatite located in khibinites on the Khibinpakhkchorr Mt. in Khibiny massif (Kola Peninsula). The radiated intergrowths of burovaite-Ca and labuntsovite-Mn were detected in caverns inside microcline in association with lemmleynite-Ba, analcime, apophylite, etc. Mean composition of the mineral (wt %): Na2O 3.72, K2O 2.76, CaO 4.22, SrO 0.47, BaO 0.23, MnO 0.01, Fe2O3 0.30, Al2O3 0.14, SiO242.02, TiO2 17.30, Nb2O5 15.21, H2O (meas.) 12.60; total sum 98.98. Its empirical formula was calculated for [(Si,Al)16O48] as following: {(Na3.10 K1.07Ca0.37Sr0.04Ba0,.04)4.62}(Ca1.28Zn0.01)1.29(Ti4.97 Nb2.56Fe0.08Ta0.02)7.63(Si15.93Al0.07)16O48(OH6.70O0.93)7.63·12H2O. The most intensive lines of X-ray powder diffraction pattern of burovaite-Ca [I-d Å]: 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; 70—1.444. The structure of burovaite-Ca was solved by A. A. Zolotarev, jr. The mineral is monoclinic, space group C2/m. Unit cell parameters: a = 14.529(3), b = 14.203(3), c = 7.899(1), â = 117.37(1), V = 1447.57 Å3. Burovaite-Ca is the isostructural Ti-dominant analogue of karupmøllerite-Ca and gjerdingenite-Ca. There were defined in host pegmatite two stages of mineral-forming — the mere pegmatite and hydrothermal ones. The hydrothermal stage included some sub-stages: potassium-barium-sodium, sodium-potassium-calcium and sodium-strontium. Burovaite-Ca is related to the intermediate — sodium-potassium-calcium sub-stage. During the first one labuntsovite-Mn and lemmleynite-Ba have been formed, during the final sub-stage — tsepinite-Na, paratsepinite-Nd and tsepinite-Sr. Thus, the consequence of crystallization of the labuntsovite group minerals shows the replacement of a potassium regime of the solutions alkalinity by the sodium one in development of the host pegmatite.

[Marco E. Ciriotti]

Referenza:
• Azarova, Yu.V., Shlyukova, Z.V., Zolotarev, A.A., Jr., Organova, N.I. (2009): Burovaite-Ca, (Na,K)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O-the new labuntzovite group mineral and its position in lowtemperature mineral-forming processes within pegmatites of Khibiny massif, Russia. Geology of Ore Deposits, 51, 774-783.

Abstract:
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)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O. 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 Na2O, 2.76 K2O, 4.22 CaO, 0.47 SrO, 0.23 BaO, 0.01 MnO, 0.30 Fe2O3, 0.14 Al2O3, 42.02 SiO2, 17.30 TiO2, 15.21 Nb2O5, 12.60 H2O (measured); the total is 98.98. Its empirical formula has been calculated on the basis of [(Si,Al)16O48]: {(Na3.10K1.07 Ca0.37Sr0.04Ba0.04)4.62}(Ca1.28Zn0.01)1.29(Ti4.97Nb2.56Fe0.08Ta0.02)7.63(Si15.93Al0.07)16O48(OH6.70O0.93)7.63·12H2O. 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), = 117.37(1)°, V = 1447.57 Å3. 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.