Vermiculite

About: Vermiculite is a research topic. Over the lifetime, 2320 publications have been published within this topic receiving 37142 citations.

Some Notes on Clay Minerals in Podzol Profiles in Fennoscandia

Abstract: Montmorillonite is found to be a predominant clay mineral in the < 2/z fraction of the A2 horizon of podzol profiles in Fennoscandia, even when these are only 300 years old. Irt fractions between 2/~ and 20/~ vermiculite and. hydrobiotite predominate, but are rarely detected in the fraction coarser than 20/z. Vermiculite and hydrobiotite are also found in the finer fractions of the B horizon, but are only rarely detected in the C horizon where their presence is apparently due to contamination with interglacial or older products of weathering. The presence of kaolinite in some profiles is explicable in the same way.

Changes in soil mineralogy and exchangeable cation pools in stands of Norway spruce planted on former pasture land

Abstract: Chemical and mineralogical properties of the soils in 35- and 70-year-old stands of Norway spruce (Picea abies (L.) Karst), planted on former pasture and were studied at Asa Experimental Forest, southern Sweden. Remnant deciduous forests bordering the spruce stands were used as controls to assess possible tree-species-related effects on soil development. All soils are acid with little difference in soil pH between the spruce and deciduous stands. However, the saturation of the exchange complex with Mg is lower beneath spruce and the total exchangeable Mg pool in the upper meter of these soils is one third of the Mg store beneath the deciduous stands. Amphibole, biotite and chlorite are the major sources of Mg in the parent soil. The clay fraction of the topsoil beneath spruce has been depleted of all these easily weatherable ferromagnesian minerals. Apart from weathering-resistant primary silicates, the clay fraction consists almost exclusively of expandable, smectitic mixed-layer minerals, which are believed to be the products of advanced stages of biotite weathering. In contrast, vermiculite is the dominant secondary mineral in the A-horizon in the deciduous stands, and some chlorite has survived. Moreover, a greater depth of in situ weathering is indicated for the soil of the old spruce stands where biotite/vermiculite mixed-layers have formed in the C-horizon as products of early stages of biotite weathering. Thus, differences between the paired sites in soil solution chemistry are supported by the qualitative differences in soil mineralogy, and are believed to reflect divergent biotic and/or abiotic processes in the different stand types.

Biotite-controlled linear compositional weathering trends in tonalitic to quartz dioritic saprock, Santa Margarita Ecological Reserve, southern California, USA

Abstract: Geochemical data derived from saprock produced by the weathering of K-feldspar-absent or K-feldspar-poor tonalite to quartz diorite yield linear compositional weathering trends pointed away from the p(K)-apex in p(A)–p(CN)–p(K) ternary diagrams. In contrast, published geochemical data derived from the classical granodioritic Toorongo weathering profile of south Australia yields a linear compositional weathering trend pointed away from the p(CN)-apex. The latter plagioclase-dominated weathering trend has been recognized since about 1984 and is due to the removal of CaO and Na2O from plagioclase. In contrast, to our knowledge, the biotite-dominated weathering trend derived from K-feldspar-absent to K-feldspar-poor tonalite to quartz diorite has not been documented or recognized previously, and is likely due to the removal of K2O from the interlayer position of biotite as it is transformed into vermiculite or mixed-layer biotite/vermiculite.