Charoite, a new mineral and a new jewelry stone

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    Charoite, a new mineral and a new jewelrystoneV. P. RogovaPublished online: 29 Jun 2010.

    To cite this article: V. P. Rogova (1979) Charoite, a new mineral and a new jewelry stone, InternationalGeology Review, 21:5, 615-620, DOI: 10.1080/00206818209467101

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  • Charoite, a new mineral and a new jewelry stone1

    V.P. Rogova ef al.

    The mineral is named for the region of its occurrence - the middle course of the Chary River. The deposit of charoite is localized within the Murun syenite massif, occurring at the junction of the Aldan crystalline shield and the Siberian Platform. The southern part of the massif (Greater Murun) cuts Archean crys-talline schists and gneisses; the northeastern part ( Lesser Murun), Cambrian marly lime-stones and dolomites. Rocks of the Murun Massif belong to a Mesozoic magmatic complex. The Aldan Shield is also similar in petrochemi-cal features to rocks of the intrusive of the Central Aldan region (Bilibin, 1959). The formation of the massif occurred in three phases. The earliest formations are flows of trachyte and pseudoleucite trachyte, having limited distribution. The flows of effusives are cut by intrusive alkalic rocks, consisting of nepheline - and aegirine - syenites, forming the main part of the massif. The magmatic stage is concluded by the injection of a dike complex, in which there are present alkalic pegmatites, pseudoleucite tinguaites, solvs-bergites, and grorudites. Pseudoleucite effu-sive, intrusive, and vein rocks, both melano-cratic and leucocratic, are widely developed within the Lesser Murun (Rogova, 1966).

    In the pseudoleucite rocks there are present in variable amounts K-feldspar, kalsilite, mel-anite, aegirine, apatite, and a ra re zirconium silicate, wadeite (Rogova and Sidorenko, 1964).

    In the border parts of the massif, and also within the zone of tectonic disturbance, wide bands of K-feldspar metasomatites are de-veloped. In metasomatites enriched in K at the contact with limestone there were formed un-usual K-Ca minerals: charoite, canasite, and tinaksite (Rogov et a l . , 1965). The tempera-ture of homogenization of gas-liquid inclusions

    Considered and recommended for publication by the Commission on New Minerals and Mineral Names, All Union Mineralogical Society, Oct. 27, 1976. Recommended by the Commission on New Minerals, IMA, June 22, 1977.

    Translated by Michael Fleischer from Charoitnovyy mineral i novyy yuvelirno-podelochnyy kamen', Vses. Mineralog. Obshch. Zapiski, 1978, no. 1, p. 94-100. Co-authors with Rogova are Yu.G. Rogov, V.A. Drits, and N.N. Kuznetsova.

    in tinaksite is 400 C. Charoite- and K-feldspar-containing metasomatites have been aegirinized.

    Charoite is the principal rock-forming mineral in the metasomatites and constitutes 50-90% of the rock (fig. 1). It is sometimes developed along the periphery of platy crystals of canasite or fills interstices between them.

    The color of charoite is lilac of various shades to violet. Density 2. 54, hardness (PMT-3, load 50g, 12 measurements) 412 6 kg/mm2. Charoite forms finely fibrous aggregates with vitreous luster; in aggregates with parallel fibrous structure there is observed silky luster. The mineral is insoluble in acids. On crushing elongated fragments with rectangu-lar boundaries are formed. Cleavage is average in three directions. The angle between the planes of prismatic cleavage is 124; the angle between the planes of the prismatic and pina-coidal cleavages on (001 \ is 104.

    The optical properties of charoite were studied in immersion preparations and in thin sections. The mineral is biaxial, positive, colorless in section. In thick fragments in immersion it is pleochroic: Z colorless, X rose-colored. The dispersion of the optic axes is variable. Indices of refraction were mea-sured in optically oriented sections: y = 1. 559 0. 002, 0 = 1 . 553 0. 002, a = 1. 550 0.002, y - a = 0.009, 2V = 28-30 (mea-sured on the Fedorov stage). Elongation posi-tive, X = b, Z c = 5 (fig. 2). The optical properties permit one to assume that the min-eral is monoclinic. In physical properties the mineral differs from canasite, similar in chem-ical composition ( Dorfman et a l . , 1959).

    For chemical analysis (table 1) fine t rans-parent plates of the new mineral were selected under the binoculars. The homogeneity of charoite was confirmed by electron microscope study ( suspension method): aggregates of the mineral consist of homogeneous elongated particles of rectangular form (fig. 3). Spec-trograph^ analysis showed the following in the mineral: tenths of a percent of Pb, La, and Mn; thousandths of a percent of Zr and Y. Ba, Sr, and Mn are distributed uniformly in charoite (fig. 4). Analysis 3 (table 1) was calculated to the following formula: ( Cai. 57 Nao. 5lKo. 93Sro. 03Bao. 07) 3. 11 (Si40io) ((OH) 0. 58FQ. 28) 0. 78' 0- 72H20, Z = 18.

    Internat. Geology Rev., v. 21, no. 5 IGR is not registered with the Copyright Clearance Center, Inc.

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  • INTERNATIONAL GEOLOGY REVIEW

    FIGURE 1. Finely fibrous aggregate of charoite. Thin section, nicols crossed, x 60.

    Hj4

    (010)

    FIGURE 2. Optical orientation of charoite.

    If one assumes that the AI2O3 found in analyses 1 and 2 (table 1) is bound to mechan-ical admixtures of anorthoclase, the following formulas of charoite are obtained:

    Anal. 1 - (Ca11)3-35

    [Si4O10] (OH) 0.52H2O,

    Anal. 2 - (Cai.68Na0436K0.70Sr0>09Ba0.09).,.9,

    [Si4O10] [(OH)0.fllF0>17]0.78 1.00H2O.

    In the formulas of charoite the number of univalent anions is identical ( small differences are explained by the isomorphism of hydroxyl and F ) , very close to their sum ( K + H20), but significantly more noticeable are the dif-ferences of the total contents of univalent - and divalent - cations. These data permit one to assume that in the structure of charoite an in-crease of the content of divalent cations, the K position may be occupied by a molecule of H2O.

    The new mineral differs from the chemically similar canasite ( Ca5Na4K2) n [Sii203o](OH, F) 4, not only by a notable admixture of barium, strontium, and the presence of molecular water, but also by a different total content of cations, and also additional anions, entering into a silicon-oxygen radical (Si4Ol0) - Table 1.

    Comparing the infra-red spectra of charoite and canasite2, from the Khibina Massif (fig. 5), both minerals are observed to show a triplet in the region of the valence oscillation Si-O, thereby for canasite the absorption peaks are of approximately equal intensity, whereas for charoite the low wave-lengths are more intense and the high wave-lengths have minimum intens-ity. The infra-red spectra of the compared minerals also differ considerably in the region 400-800 cm-1, and also in the regions of the hydroxyl oscillation. Canasite has an absorp-tion peak at 3600 c m _ l , but there is not observed absorption in the region of the deformational oscillation of water at 1600-1700 cm-1. This fact permits one to assume that the main part of the water in canasite occurs in the form of OH groups. For charoite, in the region of valence oscillation of hydroxyl there are four peaks: 3410, 3500, 3550, and 3610 cm-1. Be-sides, in the region of deformational oscillation there is observed an intense, slightly resolved triplet: 1590, 1620, and 1650 cm-1. This feature of the infra-red spectrum of charoite permits one to assume that, in distinction from canasite, most of the water in the struc-ture of the new mineral occurs in molecular form, possibly of zeolitic type with different energetic characteristics.

    2Sample 70754 of canasite from the Miner