ALBERT

Description: Zoned crystals of carbocernaite occur in hydrothermally reworked burbankite-fluorapatite-bearing calcite carbonatite at Bear Lodge, Wyoming. The mineral is paragenetically associated with pyrite, strontianite, barite, ancylite-(Ce), and late-stage calcite, and is interpreted to have precipitated from sulfate-bearing fluids derived from an external source and enriched in Na, Ca, Sr, Ba, and rare-earth elements (REE) through dissolution of the primary calcite and burbankite. The crystals of carbocernaite show a complex juxtaposition of core-rim, sectoral, and oscillatory zoning patterns arising from significant variations in the content of all major cations, which can be expressed by the empirical formula (Ca 0.43–0.91 Sr 0.40–0.69 REE 0.18–0.59 Na 0.18–0.53 Ba 0–0.08 ) 1.96–2.00 (CO 3 ) 2 . Interelement correlations indicate that the examined crystals can be viewed as a solid solution between two hypothetical end-members, CaSr(CO 3 ) 2 and NaREE(CO 3 ) 2 , with the most Na-REE-rich areas in pyramidal (morphologically speaking) growth sectors representing a probable new mineral species. Although the Bear Lodge carbocernaite is consistently enriched in light REE relative to heavy REE and Y (chondrite-normalized La/Er = 500–4200), the pyramidal sectors exhibit a greater degree of fractionation between these two groups of elements relative to their associated prismatic sectors. A sample approaching the solid-solution midline [(Ca 0.57 Na 0.42 ) 0.99 (Sr 0.50 REE 0.47 Ba 0.01 ) 0.98 (CO 3 ) 2 ] was studied by single-crystal X-ray diffraction and shown to have a monoclinic symmetry [space group P 11 m , a = 6.434(4), b = 7.266(5), c = 5.220(3) Å, = 89.979(17)°, Z = 2] as opposed to the orthorhombic symmetry (space group Pb 2 1 m ) proposed in earlier studies. The symmetry reduction is due to partial cation order in sevenfold-coordinated sites occupied predominantly by Ca and Na, and in tenfold-coordinated sites hosting Sr, REE, and Ba. The ordering also causes splitting of carbonate vibrational modes at 690–740 and 1080–1100 cm –1 in Raman spectra. Using Raman micro-spectroscopy, carbocernaite can be readily distinguished from burbankite- and ancylite-group carbonates characterized by similar energy-dispersive spectra.

Description: Rowleyite, $$[\mathrm{Na}{({\mathrm{NH}}_{4},\mathrm{K})}_{9}{\mathrm{Cl}}_{4}]{[{\mathrm{V}}_{2}^{5+,4+}(\mathrm{P},\mathrm{As}){\mathrm{O}}_{8}]}_{6}\cdot n[{\mathrm{H}}_{2}\mathrm{O},\mathrm{Na},{\mathrm{NH}}_{4},\mathrm{K},\mathrm{Cl}]$$ , is a new mineral species from the Rowley mine, Maricopa County, Arizona, U.S.A. It was found in an unusual low-temperature, apparently post-mining suite of phases that include various vanadates, phosphates, oxalates, and chlorides, some containing $${\mathrm{NH}}_{4}^{+}$$ . Other secondary minerals found in association with rowleyite are antipinite, fluorite, mimetite, mottramite, quartz, salammoniac, struvite, vanadinite, willemite, wulfenite, and several other potentially new minerals. Analyzed 13 C values for the antipinite in association with rowleyite are consistent with a bat guano source. Crystals of rowleyite are very dark brownish green (appearing black) truncated octahedra up to about 50 μm in diameter. The streak is brownish green, the luster is vitreous, very thin fragments are transparent. The Mohs hardness is about 2, the tenacity is brittle, fracture is irregular, there is no cleavage, and the measured density is 2.23(2) g/cm 3 . Rowleyite is optically isotropic with n = 1.715(5). Electron microprobe analyses yielded the empirical formula $${[{({\mathrm{NH}}_{4})}_{8.81}{\mathrm{Na}}_{3.54}{\mathrm{K}}_{2.58})}_{\Sigma 14.93}{\mathrm{Cl}}_{6.29}{({\mathrm{H}}_{2}\mathrm{O})}_{16}][{({\mathrm{V}}_{9.36}^{5+}{\mathrm{V}}_{2.64}^{4+})}_{\Sigma 12}{({\mathrm{P}}_{5.28}{\mathrm{As}}_{0.72}^{5+})}_{\Sigma 6}{\mathrm{O}}_{48}]$$ . Raman and infrared spectroscopy confirmed the presence of NH 4 and H 2 O. Rowleyite is cubic, $$Fd\overline{3}m$$ , with a = 31.704(14) Å, V = 31867(42) Å 3 , and Z = 16. The crystal structure of rowleyite ( R 1 = 0.040 for 1218 F o 〉 4 F reflections) contains [V 4 O 16 ] 12+ polyoxovanadate units that link to one another via shared vertices with [(P,As)O 4 ] 3– tetrahedra to form a 3D framework possessing large interconnected channels. The channels contain a 3D ordered [Na(NH 4 ,K) 9 Cl 4 ] 6+ salt net, which apparently served as a template for the formation of the framework. In that respect, rowleyite can be considered a salt-inclusion solid (SIS). The rowleyite framework is among the most porous known.