Journal Article•
On Iron-wollastonites in contact skarns: an example from skye
About: This article is published in American Mineralogist.The article was published on 1948-12-01 and is currently open access. It has received 10 citations till now. The article focuses on the topics: Skarn.
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TL;DR: In this article, phase relations for Mn-bearing pyroxenes and pyroxenoids were investigated using electron microprobe analysis of manganese silicates from Balmat, N.Y., and a compilation of these data along with published and unpublished analyses for phases plotting on the RSiO3 tetrahedron was provided.
Abstract: Electron microprobe analysis of manganese silicates from Balmat, N.Y., has helped elucidate phase relations for Mn-bearing pyroxenes and pyroxenoids. A compilation of these data along with published and unpublished analyses for phases plotting on the CaSiO3-MgSiO3-MnSiO3 and CaSiO3-FeSiO3-MnSiO3 faces of the RSiO3 tetrahedron has constrained the subsolidus phase relations. For the system CaSiO3-FeSiO3-MnSiO3, the compositional gaps between bustamite/hedenbergite, bustamite/ rhodonite and rhodonite/pyroxmangite are constrained for middle-upper amphibolite facies conditions and extensive solid solutions limit possible three phase fields. For the CaSiO3-MgSiO3-MnSiO3 system much less data are available but it is clear that the solid solutions are much more limited for the pyroxenoid structures and a continuum of compositions is inferred for clinopyroxenes from diopside to kanoite (MnMgSi2O6) for amphibolite facies conditions (T=650° C). At lower temperatures, Balmat kanoites are unstable and exsolve into C2/c calciumrich (Ca0.68Mn0.44Mg0.88Si2O6) and C2/c calciumpoor (Ca0.12Mn1.02Mg0.86Si2O6) phases. At temperatures of 300–400° C the calcium-poor phase subsequently has undergone a transformation to a P21/c structure; this exsolution-inversion relationship is analogous to that relating augites and pigeonites in the traditional pyroxene quadrilateral. Rhodonite coexisting with Mn-clinopyroxenes is compositionally restricted to Mn0.75–0.95Mg0.0–0.15Ca0.05–0.13SiO3. For the original pyroxene+rhodonite assemblage, the Mg and Ca contents of the rhodonite are fixed for a specific P (6kbars)-T (650° C)-X(H2O)-X(CO2) by the coexistence of talc+quartz and calcite+quartz respectively.
38 citations
TL;DR: The crystal structures of t\VO pyroxenoids having compositions Cao.5Feo.02Si03 have been refined using least-squares techniques from single-crystal x-ray intensity data measured with an a.utomatod diffractometer as mentioned in this paper.
Abstract: The crystal structures of t\VO pyroxenoids having compositions Cao.5Feo.5Si03 and approximately CaO.79Feo.19Mno.02Si03 have been refined using least-squares techniques from single-crystal x-ray intensity data measured with an a.utomatod diffractometer. Both pyroxenoids have approximately the same unit-cell paralnet~rs and stru~tures as bustamite: Space group A I; a = 7.69 A, b=7.11A, c=13.765A, ,x=90022', (3=95°19', y=103°58'; and a=7.83A, b= 7.23A, c= 13.925A,cx= 90°1', fJ= 95°24', y= 103°21' respectively. The synthetic crystal of Cao.5Feo.5Si03 has Fe and Ca ordered over two general and two special positions. Although twinning prevented an accurate determination of the cation distribution in the natural crystal of Cao.79Feo.19Mno.o2Si03, there
30 citations
TL;DR: In this paper, the miscibility gap between Mn-bustamite and Mn-wollastonite has been determined experimentally by a hydrothermal technique between 400° and 1200° C at P ≥ 2 kbar.
Abstract: In the system CaSiO3-CaMnSi2O6-CaFeSi2O6 extensive miscibility gaps between pyroxenoids and clinopyroxenes are observed. The miscibility gap between Mn-bustamite and Mn-wollastonite has been determined experimentally by a hydrothermal technique between 400° and 1200° C at P
f= 2 kbar. Further experiments have been performed at P
f=9 kbar, which revealed a shifting of the miscibility gap towards more Ca-rich compositions. The bustamite phase is stabilized by high pressures and the wollastonite structure is the stable phase at high temperatures. Similar phase relations as along the join CaSiO3-CaMnSi2O6 exist along the join CaSiO3-CaFeSi2O6 but with a more extensive two-phase field of bustamite-clinopyroxene. Possible phase relations along the joins CaSiO3-CaMnSi2O6, CaSiO3-CaFeSi2O6 and CaFeSi2O6-CaMnSi2O6 are given in temperature-composition diagrams for low pressures, based on natural and experimental data.
21 citations
TL;DR: In the western Carpathians of Romania, clinopyroxene with a very high content of the Ca-Tschermak (up to 24 wt.% Al2O3) and esseneite components occurs as veinlets and inclusions, in places associated with kalsilite, in calcite and in wollastonite very close to the marble contacts of two shallow monzodioritic intrusive complexes as mentioned in this paper.
Abstract: In the western Carpathians of Romania, clinopyroxene with a very high content of the Ca-Tschermak (up to 24 wt.% Al2O3) and esseneite components occurs as veinlets and inclusions, in places associated with kalsilite, in calcite and in wollastonite very close to the marble contacts of two shallow monzodioritic intrusive complexes, Magureaua Vatei, in the Apuseni Mountains, and Oravita-Ciclova, in Banat, both of Upper Cretaceous age. These relics originate from magmatic veinlets, emplaced at an early stage of the magmatic process and later recrystallized at high temperature (> 800 degrees C) by a CO2-dominated fluid (stage 1). Such fluid probably resulted from the reaction of calcite with the main intrusive body at the time of its emplacement, a reaction also witnessed by the development of a symplectitic association of anorthite and aluminous pyroxene at the intrusive margins, and by the (exceptional) occurrence of Na-rich melilite. Part of the intrusive boundaries were later invaded by pegmatite-forming liquids or fluids that, upon reaction with calcite, first produced idiomorphic crystals of (Fe,Mg)-rich wollastonite (stage 2), occasionally hosting minerals of stage 1, followed by the development of a fibrous wollastonite-grossular association (stage W) accompanied by an (Al-poor) diopside that progressively became Al-rich (stage P) through further modification of the fluid by reaction with calcite. The later appearance of vesuvianite initiated the large-scale postmagmatic hydrothermal process.
18 citations
Cites background from "On Iron-wollastonites in contact sk..."
...Several occurrences of ferrobustamite in skarns have been reported, e.g., at the Kagata mine, Japan (Shimazaki & Yamanaka 1973) and Skye (Tilley 1948, Rapoport & Burnham 1973)....
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01 Dec 1973
TL;DR: In this paper, Schaller et al. presented sixteen unpublished analyses of Broken Hill manganese silicates (two pyroxmangite, one rhodonite, four hedenbergite, and nine bustamite) from the papers of the late Dr W. T.Schaller, complemented with additional analyses by the electron microprobe to define the compositional fields of these minerals.
Abstract: Sixteen unpublished analyses of Broken Hill manganese silicates (two pyrox‐mangite, one rhodonite, four hedenbergite, and nine bustamite) from the papers of the late Dr W. T. Schaller are presented. They have been complemented with additional analyses by the electron microprobe to define the compositional fields of these minerals. Data are provided on the relationship of these minerals with tephroite and garnet. The occurrence of roepperite (zincian tephroite) at Broken Hill is discredited, and its validity is doubtful. Dannemorite from Broken Hill has a composition close to Mn2(Fe,Mg)5Si8O22(OH)2, and can be considered a valid amphibole subspecies.
16 citations