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Magmatic fluids and skarn mineralization: the Burdigalian As-W skarn at Karézas (Edough Massif, NE Algeria)
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
D.E. Aïssa, A. Cheilletz, C. Marignac
In the Karézas skarns are recorded (Aïssa 1996) two sequences of prograde-retrograde events (Einaudi et al. 1981), labelled “Cycle I” and “Cycle II” in Fig. 1. Cycle I resulted in the formation of zoned prograde skarns at the boundary between thick marble layers and the paragneisses. On the marble side, clinopyroxenites (ferrosalite-hedenbergite) replaced the calcite-forsterite-phlogopite primary paragenesis. On the paragneiss side, plagioclasites (An60) replaced a high-grade association (Kfs-Bt-Sil). Garnet rocks pockets and veins (consisting of grossular to andradite) are superimposed to the pyroxenites. The retrograde stage is marked by the development of calcic amphiboles and sulfides (pyrrhotite, chalcopyrite, cubanite) at the expense of clinopyroxenes. The retrograde stage resulted in a layered structure, with layers of pyrrhotite, several mm thick, within the clinopyroxenites. As some of these layers are folded at the mm scale, it is thought that the Cycle I in the Karézas skarns was coeval with the HT-LP tectonometamorphic event associated with the late Tertiary extensional process.
Metamorphic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Marble protoliths have relatively simple chemistry; they are mostly CaCO3 (calcite) or CaMg(CO3)2 (dolomite). When metamorphosed, however, the rocks often gain Ca-Mg silicate minerals such as those listed in Table 10.1. Sometimes, grossular (a kind of garnet), vesuvianite, or other Al-bearing minerals grow as well. The order of minerals in Table 10.1 is from those that generally form at lowest temperature (talc and then tremolite) to those that form at highest temperature (vesuvianite and grossular). The silica and aluminum, necessary for some of these minerals to form, come from small amounts of quartz or clay present in the parent rocks or are introduced by metasomatism.
Literature Review
Published in Habeeb Lateef Muttashar, Sustainable Construction Materials, 2019
Varieties of garnet minerals exist, each having its characteristic chemical composition. The predominant minerals in the garnet group are almandine, pyrope, spessartine, andradite, grossular, and uvarovite. All these minerals possess vitreous luster, varying diaphaneity from transparent to translucent, brittle tenacity, and a lack of cleavage. They occur in the form of individual crystals, stream-worn pebbles, granular aggregates, and massive clusters (Evans, 2006). The chemical formula, hardness, specific gravity, and colors of these garnets are summarized in Table 2.4.
Origin and evolution of nephrites, diopsidites and giant diopside crystals from the contact zones of the Pounamu Ultramafics, Westland, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
Giant diopsides grew in a geologically-young extensional fracture, nucleating on diopside-rich segregations formed by rodingitisation along a meta-serpentinite-schist contact within the Pounamu Ultramafics. With crystallisation temperatures likely to be considerably lower than those of the earlier Alpine metamorphism, the dominance of diopside relative to tremolite suggests crystallisation from H2O-rich fluids (Spear 1993). The diopsidite mineral assemblages at Mt Inframeta also contain the aluminous phases grossular-andradite-rich garnet (with variable uvarovite component) and an epidote group mineral with a variable Fe component. Gordon and Greenwood (1971) showed that at a nominal pressure of 2 kb, the zoisite-grossular assemblage is restricted to fluid compositions with XCO2 of < 0.06. Taylor and Liou (1978) have subsequently shown that the addition of Fe extends the stability field of andradite and epidote relative to grossularite and zoisite, but at pressures of 2 kb, the fluid composition at temperatures less than 500° C is still H2O-dominated, with XCO2 < 0.12. All stability fields are sensitive to the effect of fO2.
Effectiveness of various polysaccharides for controlling properties of alkali-activated manganese-rich slag pastes
Published in European Journal of Environmental and Civil Engineering, 2022
Shehzad Mussawar, Muhammad Ali Sikandar, Zafar Baloch, Amjad Naseer, Syed Azmat Ali Shah
Other hydration products similar to alkali-activated BFS were also observed, including killalaite (2Ca3⋅Si2O7⋅H2O), which is a C-S-H-type gel. In addition to killalaite, chains of crystalline minerals such as hydrogrossulars and hydrogarnets, zeolitic phases, and mica phases were also identified. The calcium aluminate garnet series known as hydrogrossular includes grossular (Ca3Al2(SiO4)3), hibschite (Ca3Al2(SiO4)1.25(OH)7), katoite (Ca3Al2(OH)12), etc. Similarly, zeolitic phases were observed in these specimens are natrolite (Na2Al2Si3O10⋅2H2O) and gismondine (CaAl2Si2O8.4H2O). The mica phase observed was Nepheline (NaAlSiO4). Glukhovsky et al. (1980) also observed the hydrogrossular, zeolitic, and mica phases in hydrated alkali-activated slags in an XRD analysis.
Metamorphism in the New England Orogen, eastern Australia: a review
Published in Australian Journal of Earth Sciences, 2020
K. Jessop, N. R. Daczko, S. Piazolo
Contact metamorphism is associated with intrusive rocks of this phase. A study of Late Triassic granitoids that intrude the Nambucca and Hastings blocks (Kinny, Leitch, & Vallance, 1985; Leitch, Milligan, & Price, 1982; Och et al., 1998) outlined both thermal highs surrounding the plutons, and hotspots thought to reflect granitoids at shallow depth. The contact metamorphic overprint grades from randomly oriented flakes and decussate clumps of biotite in metasedimentary rocks, to completely recrystallised spotted hornfels. Adjacent to the plutons, pelitic rocks contain quartz–biotite–muscovite–cordierite and calcareous rocks contain quartz–diopside–wollastonite–grossular–vesuvianite. Och et al. (1998) identified three mineral isograds surrounding the Carrai Granodiorite; biotite-in ∼1200 m, cordierite in ∼600 m and cordierite–K-feldspar ∼100 m from the pluton boundary. P/T conditions were calculated to be T ∼550 °C and P ∼1 kbar (Kinny et al., 1985). Figure 10 shows the outline of contact aureoles mapped by Kinny et al. (1985) and identifies other plutons of this phase that have recorded aureoles.