Serpentine composition

Based on their experimental study of a serpentine composition at high pressures and temperatures, Stalder and Ulmer (2001) argue that chondrodite would only be stable in ultramafic compositions with >2 wt.% H2O. 

Stalder R. and Uhner P. (2001) Phase relations of a serpentine composition between 5 and 14 GPa significance of chnohumite and phase E as water carriers into the transition zone. Contrib. Mineral. Petrol. 140, 670—679. (also cf. errata Contrib. Mineral. Petrol. 140, 754). 

Figure 20.14 SEM images of the worn surface of PlTE/serpentine composites at different loads (a) 1.43 MPa, (b) 4.28 MPa, and (c) 8.55 MPa.

Jia, Z., Yang, Y., Chen, J., Yu, X., 2010. Influence of serpentine content on tribological behaviors of PTFE/serpentine composite under dry sliding condition. Wear 268, 996—1001. 

Jia, Z.N., Hao, C.Z., Yang, Y.L., 2014. Tribological performance of hybrid PTFE/serpentine composites reinforced with nanoparticles. Tribology 8, 139—145. 

A number of serpentine group minerals have substitutions in both the tetrahedral and octahedral layer, but they stiU maintain electrostatic neutraUty. Amestite [12413-27-5] which approximates (Mg2Al)(SiAl)0 (0H)4 in composition, cronstedite [61104-43-3] (Fe " 2 Fe " )(SiFe " )0 (0H)4, chamosite,... 

Chlorite is another mineral that is commonly associated with mixed-layered clays. Complete soHd solutions of chlorite mixed-layer minerals have not been identified. In contrast to iUite—smectite mixed-layer minerals, chlorite mixed-layer minerals occur either as nearly equal proportions of end-member minerals (Rl) or dominated by one end member (RO) (142). Mixed-layer chlorite may consist of any of the di—tri combinations of chlorite and chlorite mixed-layering occurs with serpentine, kaolinite, talc, vermicuhte, smectite, and mica. References of specific chlorite mixed-layer minerals of varied chemical compositions are available (142,156). 

The bedrock source of the 10s to 100s of Cr-diopside grains in tiii across the region has not yet been found, in spite of the predominance of pyroxenites and peridotites in the TNB, remnants of primary Cr-diopside are scarce because most rocks have been metamorphicaiiy and metasomaticaiiy aitered such that serpentine has repiaced oiivine and orthopyroxene and amphiboie, chlorite, talc and carbonate has replaced clinopyroxene. Be-cause the Cr-diopside source is unknown, their compositional range and relationship to Ni-mineralization cannot be determined. 

The crystal structures of all the minerals in the serpentine group contain the same basic building blocks. The basic unit is composed of a silicate sheet of composition (Si205) ", in which three of the O atoms in each tetrahedron are shared with adjacent tetrahedra (Fig. 2.2A), and a nonsilicate sheet of... 

Table 2.2 The Major Serpentine Group Minerals Composition, Polytype, and Unit Cell Dimensions... 

Fig. 2.2A Schematic representation of the structural components of the serpentines. The tetrahedral (T) sheet. The composition can be expressed as [(Si205) ] , is formed when three of the four oxygens in the tetrahedon are shared. The large open Circles represent oxygen ions the small solid circles are silicon ions. The open circles concentric with the silicon atoms represent oxygen atoms located vertically, above the silicon (apical oxygens).

Antigorite is another serpentine mineral. It is similar in composition to chrysotile except that small amounts of Fe substitute for some of the Mg" in its structure (see Table 2.2). This subtle difference in composition produces a limited sheet structure with corregated stacking of the octahedral-tetra-... 

Two to 3 percent of the world s total asbestos production has been of the crocidolite variety, most of which has come from South Africa. Western Australia was a minor producer of crocidolite between 1944 and 1966. All amosite has been mined in the Transvaal Province of South Africa (2 to 3 percent of the world total). The only significant anthophyllite production came from Finland, where about 350,000 tons were mined between 1918 and 1966. Table 2.6 lists the composition, optical, and diffraction characteristics of the six asbestos minerals. More information on individual mineral species can be found in the references accompanying the sections on serpentine and amphibole types. Discussion of the geology, terminology, and exploitation of the several types of asbestos can be found in Ross (1981). 

Silicate minerals that usually occur as spherulitic aggregates of fibers have formed as a result of the alteration of the many minerals subsumed within the category of biopyriboles. Alteration of the micas under hydrothermal conditions produces compositional variants on recrystallization such as hydrous muscovite. Some of these samples have been labeled asbestiform, probably because they are found in veins that criss-cross rock masses. Fibrous micaceous minerals also occur as discrete disseminated particles, although few detailed analyses of crystallites from the disperse occurrences have been made. Fibrous mica found in veins usually grades (composition-ally) into members of the serpentine mineral group, the clays or the chlorites. 

Figure 1. Representation of the ideal compositions of some major phyllosilicate phases in the MR - 2R - 3R coordinates. M = muscovite, paragonite P - phlogopite Py = pyrophyllite Kaol = kaolinite S serpentine T = talc Chlor = chlorite, 14 8 or aluminous 7 8 polymorphs Ce = celadonite F = feldspar.

Sepiolite and palygorskite have a rather special composition and seem to be related to specific mineral parageneses. They appear to be stably associated with montmorillonite, corrensite, serpentine, chert, sulfates, carbonates and various salts. They are found in deposits typified by processes of chemical precipitation or solution-solid equilibria (Millot, 1964) and are therefore rarely associated in sediments with large quantities of detrital minerals. Their chemical environment of formation is in all evidence impoverished in alumina and divalent iron. Their frequent association with evaporites, carbonates and cherts indicate that they came from solutions with high chlorinity. 

The most common IDPs are black objects having approximately solar elemental composition except for very volatile elements such as the noble gases. There are panicles that deviate strongly from this pattern but they are rare and are usually dominated by a single mineral such as FeS. olivine, or FeNi metal. Most of the panicles can be grouped into two classes one contains hydrated minerals such as serpentine and smeclile the other, ones that are anhydrous. 

Type I (OT) silicates include kaolinite, Al2Si205(0H)4 (Section 10.3.21) and dickite with the same composition. These are true clay minerals. Clay minerals are layer silicates with a grain size < 2 pm. The serpentines also are Type I minerals, include antigorite, Mg3Si2Os(OH)4 (Section 10.3.20) and chrysotiles with the same composition. Chrysotiles include clinochrysotile and orthochrysotile. 

The two layer silicates are divided into the kaolinite (dioctahedral) and serpentine (trioctahedral) subgroups. The dioctahedral minerals are hydrous aluminum silicates containing minor amounts of other constituents. The trioctahedral minerals vary widely in composition and isomorphous substitution is common however, these minerals are relatively rare and chemical data are limited. 

Bailey and Tyler (1960) have found numerous examples of aluminous serpentines associated with the iron ores from Lake Superior in Michigan. Basal X-ray spacings indicate various compositions, ranging from (Si3.sAlo.s)(Mgs.5Al0.s)0 0(OH)g to... 

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