Wollastonite, crystal structure

Among the first applications of DAS and DOR were O studies of crystalline silicates, in which spectacular gains in resolution of up to two orders of magnitude were obtained (Chmelka et al. 1989, Mueller et al. 1991, Mueller et al. 1992). In the case of wollastonite, nine sites were resolved, in agreement with the site multiplicity expected from the crystal structure (Figure 6.4). The use of field-dependent data to deduce isotropic information from changes in the isotropic position has now been supplemented by MQ MAS NMR. In the second dimension of the 2D DAS and MQ data sets... 

Description Natural P-wollastonite changes to a-type on heating to 1100°C synthetic grade is a-wollastonite, has very low loss on ignition, retains crystal structure during heating, giving constant chemical composition ... 

Mamedov Belov (1956) Mamedov, K.S. Belov, N.V The crystal structure of wollastonite Doklady Akademii Nauk SSSR 107(1956) 463 66... 

The crystal structure of Wollastonite has been investigated using X-ray diffraction [93,95]. It is found that Wollastonite has two different crystallographic forms. The primary crystalline form, which is found in massive natural deposits, has a triclinic unit cell and was found by Peacock [96] to be ... 

Wollastonite is calciiun sihcate with a triclinic crystal system (P21). It has infinite-chain structure, with three tetrahedra per unit cell arranged parallel to y, this repeat unit consists of a pair of tetrahedra joined apex to apex as in the [Si07] group, alternating with a single tetrahedron with one edge parallel to the chain direction. Steady-state luminescence of wollastonite has been previously studied and luminescence of Mn, Fe and supposedly Cr has been proposed (Min ko et al. 1978). 

The silicate group Si207, ordered along one direction, and having the possibility of wollastonite chains formation, is the basic element of the stracture of these silicates. The lack of some individual SiO in this chain does not change the basic structure. This is the source of variable C/S molar ratio not only in the amorphous calcium silicate hydrates but also in the relatively well crystallized tobermorite in which the tendency for increasing C/S ratio is observed [160],... 

The structure of wollastonite is characterized by chains formed from silica tetrahedra connected side-by-side through calcium in octahedral coordination [2]. These chain arrangements account for the formation of acicular crystals and preservation of their shape upon cleavage (Figure 14.1). The moderate value of wollastonite Mohs hardness (4.5-5) is attributed to the high density of the silica chains. In addition to the most important property of acicular shape, the plastics industry places high value on properties such as... 

Apart from AlPO crystals, other phosphates with structural similarities to silicates have also been determined. For example, Mg2(P20y) is isotypical with thortveitite, Sc2(Si20y). A similar isotypical relationship is also valid for Na P-wollastonite, Ca (SigOjg). 

Tremolitic talc is a related industrial mineral that, despite its classification as a talc product, is actually a natural mineral blend with tremohte as the major component and talc as a minor component. As such, tremolitic talc has properties and uses that depend primarily on its tremolite content. The hardness and prismatic shape of tremolite crystals are derived from a structure analagous to that of wollastonite. While wollastonite is comprised of single chains of silica tetrahedra, tremolite is comprised of double chains, as depicted in Figure 12. 

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