Search

Diomignite (Li2B4O7) is discredited as a mineral species, and this discreditation has been approved by the International Mineralogical Association, Commission on New Minerals, Nomenclature and Classification. Diomignite was originally reported to occur in virtually every crystal-rich inclusion in spodumene from the Tanco pegmatite in southeastern Manitoba, Canada. However, detailed study of 30 randomly selected crystal-rich inclusions in the purported type material deposited at the U.S. National Museum of Natural History, 30 inclusions in the purported type material from the American Museum of Natural History, and several hundred inclusions in self-collected samples reveals that diomignite is absent in every inclusion examined. Because no holotype specimen exists and no neotype sample was provided by the surviving authors of the original description, the presence of diomignite could not be validated. The evidence provided in the original description to the IMA in 1984 is shown to be insufficient to support the existence of diomignite as a mineral species. The previously reported boron-rich (12 mass% B2O3) composition of the melt represented as crystalrich inclusions in spodumene and petalite from the Tanco pegmatite was predicated on the assumption that diomignite is a common daughter mineral that occurs in most inclusions and that the inclusions are primary melt inclusions. The nonexistence of diomignite, and the absence of other borate daughter minerals, in these crystal-rich inclusions indicates that the boron content was greatly overestimated and so comparisons to experimentally generated boron-rich (>10 mass% B2O3) boundary-layer melts are unwarranted. Furthermore, the discreditation of diomignite negates the inferred role of a Li2B4O7- flux-rich melt in the generation of primary pegmatite textures and rare element oxide mineralization in the Tanco pegmatite. [ABSTRACT FROM AUTHOR]

Aluminum hydroxysulfate, AlSO4(OH), is postulated to play a vital role in controlling the solubility of aluminum in sulfate-rich acidic soils and ground waters, but it has not yet been confirmed in nature. This study reports the synthesis of an AlSO4(OH) crystal at 700 °C and ~1.0 GPa in a hydrothermal diamond-anvil cell from a mixture of 95% H2SO4 and Al2O3 powder and its structure determination from single-crystal X-ray diffraction data. AlSO4(OH) is monoclinic with space group C2/c and unitcell parameters a = 7.1110(4), b = 7.0311(5), c = 7.0088(4) Å, b = 119.281(2)°, and V = 305.65(3) Å ³. Its crystal structure is characterized by kinked chains of corner-sharing AlO6 octahedra that run parallel to the c-axis. These chains are linked together by SO4 tetrahedra and hydrogen bonds, forming an octahedral-tetrahedral framework. Except for the numbers and positions of H atoms, AlSO4(OH) is isostructural with the kieserite-type minerals, a subgroup of the titanite group of minerals. A comparison of powder X-ray diffraction patterns indicates that our AlSO4(OH) is the same as that obtained by Shanks et al. (1981) through hydrolysis of Al2(SO4)3 solutions at temperatures above 310 °C. To date, AlSO4(OH) has been synthesized only at temperatures above 290 °C, implying that it may not stable in low-temperature environments, such as acidic soils and mine waters. The possible environments to find Al(OH)SO4 may include places where sulfur-rich magma-derived fluids react with aluminous rocks under elevated temperature and pressure, and on Venus where a sulfur-rich atmosphere interacts with surface rocks at temperatures above 400 °C. [ABSTRACT FROM AUTHOR]

A series of X-ray absorption spectroscopy (XAS) experiments were made to determine the structure and stability of aqueous REE (La, Nd, Gd, and Yb) chloride complexes to 500 °C and 520 MPa. The REE3+ ions exhibit inner-sphere chloroaqua complexation with a steady increase of chloride coordination with increasing temperature in the 150 to 500 °C range. Furthermore, the degree of chloride coordination of REE3+ inner-sphere chloroaqua complexes decreases significantly from light to heavy REE. These results indicate that steric hindrance drives the reduction of chloride coordination of REE3+ inner-sphere chloroaqua complexes from light to heavy REE. This results in greater stability and preferential transport of light REE3+ over heavy REE3+ ions in saline hydrothermal fluids. Accordingly, the preferential mobility of light REE directly influences the relative abundance of REE in rocks and minerals and thus needs to be considered in geochemical modeling of petrogenetic and ore-forming processes affected by chloride-bearing hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the hydration structure of lanthanum (La) ion in aqueous nitrate solutions in a hydrothermal diamond anvil cell. Use of X-ray absorption fine structure (XAFS) technique; Analysis of XAFS data; Comparison of results with previous studies of La hydration at room temperature.

Describes an adaptation of the spindle stage for geometric analysis of fluid inclusions. Three-dimensional observation of fluid inclusions; Fluid inclusion phase ratios; Paleo-fracture analysis; Quantitative microanalysis; Evaluation of decrepitation behavior.