Recommended nomenclature for labuntsovite-group minerals

Abstract

The present report contains recommendations on the nomenclature of the labuntsovite-group (LG) minerals based on a crystal-structural classification. The labuntsovite group includes hydrous titanium and niobium silicates, both orthorhombic and monoclinic, with a structure characterized by a framework consisting of chains of (Ti,Nb)O-octahedra, linked by four-member rings of Si,O-tetrahedra. This framework contains open cavities occupied by H 2 O molecules and extra-framework cations. Seven subgroups are distinguished, each corresponding to different structure types. In accordance with the nomenclature recommendations, LG minerals have different root names if they belong to different subgroups, or are characterized by different prevailing cations in the (Ti,Nb)-position. The species with doubled unit cell are distinguished by the prefix "para". In the case of structurally ordered members (space groups C2/m, I2/m), separate species within each subgroup are recognized by different root names (to distinguish the members with Ti 8 Nb or Ti ‹ Nb) and by a modifier (-K,-Mn,-Mg etc., to distinguish the members with differently occupied "key" positions). Unlike zeolites, a complex substitution of extra-framework cations is possible in monoclinic LG minerals: 2C → D(H 2 O) 2 where C = K, Ba; D = Fe, Mg, Mn or Zn. Only one of these coupled sites (C or D) can be more than 50 % occupied, whereas the other is more than 50 % vacant and is not considered as the "key" (species-forming) position. In the case of structurally disordered members (vuoriyarvite series) with space group Cm and a large number of extra-framework positions, separate species are recognized in which different extra-framework cations (K, Na, Ca, Sr, Ba) are the most abundant in atomic proportions.

Burovaite-Ca, (Na,K)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8·12H2O, a new labuntsovite-group mineral species and its place in low-temperature mineral formation in pegmatites of the Khibiny pluton, Kola Peninsula, Russia

“…The strong band at 1640 cm -1 indicates a significant content of water in the mineral structure. In the region of OH stretching vibrations, the strong band with a maximum at 3400 cm -1 and a weak step at 3210 cm -1 are evidence of relatively firm hydrogen bonds formed by water molecules in the structure of the examined mineral (Chukanov et al, 2003). Table 1).…”

“…In general, the sequence of crystallization of the labuntsovite-group minerals illustrates the evolution of alkaline fluids from high potassium to high sodium rather than vice versa as was noted for most labuntsovite-bearing hydrothermal rocks of alkaline complexes (Pekov, 2001;Chukanov et al, 2003). The cause of such chemical evolution of mineral-forming fluids requires further investigation.…”

“…The middle and eastern parts of the vein have been significantly altered by hydrothermal fluids and largely consist of low-temperature minerals, which are reliable indicators of low-temperature transformation of these pegmatitic zones. Analcime develops after feldspar; natrolite, after nepheline; barrel-shaped crystals of catapleiite develop after eudialyte; apophyllite and phillipsite-Ca are the latest miner- Chukanov et al, 2003). Small inclusions of bituminous matter were found in the crystals of labuntsovite-Mn, tsepinite-Na, and paratsepinite-Na (Chukanov et al, 2005).…”

“…This collective name was given to all colorless labuntsovite-group members from this pegmatite. These minerals were found as parallel inter- 1 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.…”

Hydrochloric Acidic Processing of Titanite Ore to Produce a Synthetic Analogue of Korobitsynite

“…There are a few ways to obtain cheap titanosilicate materials: (1) to use rich titanite ore without its enrichment by flotation [19]; (2) to obtain other titanosilicates with similar photocatalytic activity but lesser temperature and time of crystallization; (3) to develop another technology that would allow a complete use of titanite. All these ways were put to use in the proposed technology of hydrochloric acidic processing of titanite to produce a synthetic analogue of korobitsynite, SKR, a rhombohedral Ti-dominant member of the labuntsovite group [20].…”