Enstatite

Li Si O enstatite [14681-78-8] MgSiO diopside [14483-19-3], CaMgSi O and woUastonite [14567-57-2], CaSiO. A number of sihcate glass-ceramic compositions are given in Table 1. 

Oxide ab Fotoform/Fotoceram Corning 8603 Enstatite Corning SlagsitaUs SlagsitaU White e Minelbite Gray... 

Fig. 2. RepHca electron micrograph of the fracture surface of enstatite—P-spodumene—zirconia glass-ceramic, showing twinning in the enstatite grains...

Pure talc is thermally stable up to 930°C, and loses its crystalline bound water (4.8%) between 930 and 970°C, leaving an enstatite (dehydrated magnesium siUcate) residue. Most commercial talc products have thermal loss below 930°C on account of the presence of carbonates, which lose carbon dioxide at 600°C, and chlorite, which loses water at 800°C. Talc is an insulator for both heat and electricity. 

Daw et al. [632] made a microscopic and crystallographic study of talc dehydroxylation. Nucleation, to yield enstatite, occurs inhomogeneously within the particles, perhaps at dislocations. Later, this product is topo-tactically orientated with respect to the reactant lattice, though with extensive faulting on the (010) plane owing to misfit, in addition to the attempt to preserve the oxygen lattice. In an isothermal study (1100— 1160 K) of the same reaction, Ward [633] found first-order obedience and the value of E determined (422 kJ mole-1) is close to that estimated for... 

Landwehr et al. (2001) extended the model of Wood and Blundy (1997) to include and Th". They measured experimentally Aj and Z)xh in a wide variety of synthetic clinopyroxene compositions in order to evaluate the crystal compositional dependence of U-Th fractionation. Their observations confirm the predictions of Wood et al. (1999), namely that as the M2 site becomes smaller, so D-m becomes smaller than Du (Figs. 1 and 11). The M2 site becomes smaller as the enstatite component of the clinopyroxene increases and Ca on M2 is replaced by Mg. Enstatite solubility in clinopyroxene increases with increasing temperature, consequently clinopyroxene coexisting with orthopyroxene will show higher Du/Dih at higher temperature. For this reason, DuIDjb increases with increasing pressure along the mantle solidus, as discussed above. 

The denotes molar, rather than weight fraction, partition coefficient. The X terms denote the cation molar fractions of Ca, Al and Mg, while the X terms denote the molar fraction of diopside and enstatite components in clinopyroxene. Note that this expression contains no explicit P-f dependence. 

Table 1.5. A mineralogical matrix (mole fractions) for the enstatite-forsterite-quartz assemblage.

Figure 1.4 A reactional assemblage enstatite-forsterite-quartz in the 2-dimensional space Si02-MgO. Enstatite can be decomposed as 3/4 forsterite plus 1/4 quartz.

Example let us consider a mineralogical assemblage made of enstatite, forsterite, quartz... 

A rock is made of 0.45 moles Si02,0.10 moles CaO, and 0.45 moles MgO, which we will describe with the composition vector v (0.45,0.10,0.45). If we consider this rock as being made of virtual forsterite (Si02, 0, 2MgO), enstatite (2Si02, 0, 2MgO), and diopside (2Si02, CaO, MgO), what is the projection vector v of the rock composition onto the enstatite-diopside plane ... 

In the virtual mineral space, the rock composition is projected onto the plane made by the vectors enstatite [0,1,0]T and diopside [0,0,1]T. Although these vectors are not orthogonal in the original oxide composition space, which can be verified by constructing the dot product of columns 2 and 3 in the matrix BT, the particular choice of the projection makes the vectors orthogonal in the transformed space. According to the projector theory developed above, we project the rock composition onto the column-space of the matrix A such that... 

Minster, J.-F., Ricart, L.-P. Allegre, C. J. (1979). 87Rb-87Sr geochronology of enstatite meteorites. Earth Planet. Sci. Letters, 42, 333-47. 

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