Silicate minerals

About: Silicate minerals is a research topic. Over the lifetime, 1794 publications have been published within this topic receiving 67064 citations.

The Effect of Chemical Reduction on the Stability of Pyrophyllite and Kaolinite in Pelitic Rocks

Abstract: The infrequent occurrence of kaolinite and especially of pyrophyllite in more evolved sedimentary rocks and low grade metamorphic facies of pelitic rocks is considered to be due to chemical controls in the bulk composition of these rocks. Hydrogen-rich organic gases are released from the original sedimentary organic materials during diagenesis and early metamorphism. These gases in turn reduce the iron present from the ferric to ferrous state. The effect of the valence change of the iron is to shift its position in the silicate minerals present. As a result, aluminum is obliged to readjust to the new conditions moving from an alumino-silicate phase to the mica and perhaps the chlorite phases. The new assemblage does not contain a hydrous alumino-silicate though both kaolinite and pyrophyllite could be stable in the physical environment of the rocks.

Simulations of the neutralizing capacity of silicate rocks in acid mine drainage environments 1

Abstract: Pyritic rocks with little or no carbonate mineral content generally produce acid mine drainage when exposed to the atmosphere and moisture. In the absence of carbonate minerals, it is often suggested that silicate minerals can provide some level of acid buffering. At the current time, databases of reaction kinetics are sufficiently detailed to allow calculations of the rates of silicate mineral dissolution reactions relative to the rate of pyrite oxidation. These types of calculations have been conducted for conditions of abiotic oxidation of pyrite by O2 to estimate the acid neutralizing capacity of silicate rock types in terms of specific mineral contents. Using the criteria of maintaining a pH > 5.0 for 10-years, these calculations yield the following results for some generalized igneous rock types.

Flotation Separation on Rare Earth Minerals and Gangues

Abstract: The flotation process of native rare earth minerals such as bastnasite, monazite, mixed minerals of bastnasite and monazite, using the new effective collector Dh was studied, respectively, and the flotation properties were described. The good qualities of the new collector Dh were revealed through comparing with other collector of rare earth minerals. The test results of different ore samples showed that at moderate pulp pH (8.5～9.5), rare earth minerals could be effectively separated from barium, calcium and silicon bearing intergrowth minerals (barite, calcite and silicate minerals) and high quality rare earth concentrates could be obtained successfully by the new collector Dh, acid silica gel, turpentine and reagents fitting together rationally. In order to determine optimum technical conditions, the effect of pulp pH, pulp temperature, pulp density and the effect of dosage of reagents (Dh and acid silica gel) on the flotation were investigated in the test. Simultaneously, the mechanism of the flotation of rare earth minerals from intergrowth minerals was explored. The infrared spectra for Dh and rare earth cation by analysis in theory showed that Dh formed chelate complex with rare earth cation and were adsorbed on the surfaces of rare earth minerals. The mechanism of the intergrowth minerals depressed by acid silica gel can be explained as gummy colloid hydrolyzed from acid silica gel which were selectively absorbed on the gangue minerals, making them hydrophilic and depressed, with pulp pH value of alkalescent.

Polymineralic Inclusions in Megacrysts as Proxies for Kimberlite Melt Evolution—A Review

Abstract: Polymineralic inclusions in megacrysts have been reported to occur in kimberlites worldwide. The inclusions are likely the products of early kimberlite melt(s) which invaded the pre-existing megacryst minerals at mantle depths (i.e., at pressures ranging from 4 to 6 GPa) and crystallized or quenched upon emplacement of the host kimberlite. The abundance of carbonate minerals (e.g., calcite, dolomite) and hydrous silicate minerals (e.g., phlogopite, serpentine, chlorite) within polymineralic inclusions suggests that the trapped melt was more volatile-rich than the host kimberlite now emplaced in the crust. However, the exact composition of this presumed early kimberlite melt, including the inventory of trace elements and volatiles, remains to be more narrowly constrained. For instance, one major question concerns the role of accessory alkali-halogen-phases in polymineralic inclusions, i.e., whether such phases constitute a common primary feature of kimberlite melt(s), or whether they become enriched in late-stage differentiation processes. Recent studies have shown that polymineralic inclusions react with their host minerals during ascent of the kimberlite, while being largely shielded from processes that affect the host kimberlite, e.g., the assimilation of xenoliths (mantle and crustal), degassing of volatiles, and secondary alteration. Importantly, some polymineralic inclusions within different megacryst minerals were shown to preserve fresh glass. A major conclusion of this review is that the abundance and mineralogy of polymineralic inclusions are directly influenced by the physical and chemical properties of their host minerals. When taking the different interactions with their host minerals into account, polymineralic inclusions in megacrysts can serve as useful proxies for the multi-stage origin and evolution of kimberlite melt/magma, because they can (i) reveal information about primary characteristics of the kimberlite melt, and (ii) trace the evolution of kimberlite magma on its way from the upper mantle to the crust.