Large pegmatite body/bodies are outcropping in the “Suhata Reka” quarry, near the town of Rakitovo. Their bulk mineral composition with dominant K-feldspar (40%), plagioclase (30%), quartz (25%) and mica (≤ 5%) is complemented by (REE+Y)-bearing association of primary and secondary accessories. Zircon, monazite, xenotime, scarce apatite and noticeable amount of garnet are among the pegmatite primary minerals. The cm-sized almandine-spessartine crystals contain numerous fractures which host secondary (REE+Y)-bearing phosphate (xenotime, cheralite) and silicate minerals (e.g. REE-epidote). Formation of the late-stage REE-mineralization in garnet is due to its hydrothermal alteration and redistribution of REE+Y in the secondary phases.
Abstract Fluor-rossmanite, ideally □(Al 2 Li)Al 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 3 F, is a new mineral of the tourmaline supergroup, found at the Krutaya pegmatite, Malkhan pegmatite field, Zabaykalskiy Krai, Western Siberia, Russia. It forms an intermediate zone up to 3 mm thick in a chemically heterogeneous, concentrically zoned, polychrome tourmaline crystal 3 × 2 cm in size. The new mineral is light pink, transparent with a white streak and a vitreous lustre. It is brittle, with conchoidal fracture. The Mohs hardness is 7. The D meas = 3.07(2) g cm –3 and D calc = 3.071 g cm –3 . Optically, fluor-rossmanite is non-pleochroic, uniaxial (–), ω = 1.647(2) and ɛ = 1.628(2) (589 nm). The empirical formula calculated on the basis of 31 anions (O+OH+F) is: X (□ 0.46 Na 0.32 Ca 0.20 Pb 0.02 ) Σ1.00 Y (Al 1.84 Li 1.05 Mn 0.05 Fe 2+ 0.02 Ti 0.02 Cr 0.01 ) Σ2.99 Z Al 6.00 T (Si 5.79 Al 0.21 ) Σ6.00 B 2.99 O 27 V (OH) 3 W [F 0.44 (OH) 0.20 O 0.36 ] Σ1.00. Fluor-rossmanite is trigonal, R 3 m ; the unit-cell parameters are: a = 15.7951(3), c = 7.08646(17) Å, V = 1531.11(7) Å 3 and Z = 3. The crystal structure is refined from single-crystal X-ray diffraction data [ R = 0.0211 for 1178 unique reflections with I > 2σ( I )]. The new mineral is a ‘fluor-’ species belonging to the X-vacant group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are those of rossmanite and fluor-elbaite, to which fluor-rossmanite is related by the substitutions W F – ↔ W OH – and X 2□ + Y Al 3+ ↔ X 2Na + + Y Li + , respectively.
Rare oxide-sulfosilicate-sulfate mineral assemblages have been identified in burned material from two spoil heaps (Kukla mine, Oslavany, and Ferdinand mine, Zastavka) in the Rosice-Oslavany coalfield, Czech Republic. The assemblages are deficient in Si and Al, and contain high amounts of fluorine and chlorine; major minerals are gypsum, anhydrite, fluorellestadite, periclase, brucite, and portlandite. Accessory minerals include magnesioferrite, Mn-rich srebrodolskite, and rare kumtyubeite, Fe,Cl-rich brearleyite/mayenite, wadalite, fluorite, cuspidine, rondorfite, and an unnamed mineral with composition Ca 4 (Mn,Fe) 2 O 7 . The assemblages are pyrometamorphic products of a dolomite-anhydrite-gypsum protolith, at T min > 800 °C. The most probable source of halogens was organic matter.
Sakhaite, ca. Ca48Mg16(BO3)32(CO3)16(HCl,H2O)2, is a rare rock-forming borate-carbonate mineral typically occurring in high-temperature, low-pressure calcareous skarns. It forms a complete solid solution with harkerite, ca. Ca48Mg16[AlSi4(O,OH)16]4(BO3)16(CO3)16(HCl,H2O)2. The solid solution can be described with the general formula
ABSTRACT Beryl (Be3Al2Si6O18) is a well-known mineral, most famously in its vivid green form of emerald, but also as a range of other colors. Prominent varieties of beryl aside from emerald include aquamarine, red beryl, heliodor, goshenite, and morganite. There has not been a significant amount of research dedicated to comparing the crystal-chemical differences among the varieties of beryl except in determining chromophoric cations. While the H2O content within structural channels of emerald has been explored, and the H2O content of individual beryl specimens has been studied, there has not yet been a study comparing the H2O content systematically across beryl varieties. In this study we consider single-crystal X-ray diffraction data and electron probe microanalyses of 80 beryl specimens of six primary varieties, to compare and contrast their crystal chemistry. Beryl cation substitutions are dominantly coupled substitutions that require Na to enter a structural channel site. The results indicate that with increasing Na content beryl varieties diverge into two groups, characterized by substitutions at octahedral or tetrahedral sites, and that the dominant overall cation substitutions in each beryl variety tend to be different in more than just their chromophores. We find that the relation between Na and H2O content in beryl is consistent for beryl with significant Na content, but not among beryl with low Na content. Natural red beryl is found to be anhydrous, and heliodor has Na content too low to reliably determine H2O content from measured Na. We determined equations and recommendations to relate the Na and H2O content in emerald, aquamarine, goshenite, and morganite from a crystallographic perspective that is applicable to beryl chemistry measured by other means. This research will help guide future beryl studies in classifying beryl variety by chemistry and structure and allow the calculation of H2O content in a range of beryl varieties from easily measured Na content instead of requiring the use of expensive or destructive methods.
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