Humite minerals

The next part of the crystallization process at temperatures above approximately 750 C was characterized by the development of the humite mineral norbergite, Mg2SiO MgF2. These crystals were produced by means of a solid-state reaction between chondrodite and the droplet-shaped glass phase, in the process of which both were entirely dissolved. The microstructure containing norbergite crystals is shown in Fig. 2-19c. 

Duke, D. A., 1963. Infrared investigation of the crystal chemistry of olivine and humite minerals Dissertation Abstr. 23 2543. 

We shall now present studies relating to the micro-twin structure performed by B. G. Hyde, who is a main proposer of the concepts of shear and micro-twin structures. One study is on the mineral humite family,the composition of which is generally expressed by nMg2SiO4-Mg(OH)2 (this has to be altered to nMg2SiO4-Mg(OH, F)2, because (OH) is often replaced by F in the minerals). In Table 2.4, the mineral name, together with the compositions and micro-twin structures proposed by the authors, are collected, the space group is Pmcn (orthorhombic) for n = odd and... 

Magnesium is a bright, silver-white alkaline earth metallic element (symbol Mg atomic no. 12). It is widely found as different salts in minerals such as boracite (borate), ankerite and dolomite (carbonates), carnallite (chloride), brucite (hydroxide), periclase (oxide), lazulite (phosphate), amphibole, cummingtonite, enstatite, gamierite, hornblende, humite, hypersthenite, iolite, jade, meUlite, monticellite, olivine, Pennine, saponite, sapphire, serpentine, talc, and tremolite (silicates), and epsomite, kainite, kieserite, and polyhalite (sulfates). 

The accuracy of data for fluorine obtained by EMPA, SIMS, and SREF in humite group minerals was discussed by Ottolini et al. [63], Discrepancies of fluorine data between EMPA (standard fluorite F-A a,TAP no APF corrections) and SIMS were detected in vesuvian-ites and micas [64,65]. The former are systematically lower than the latter. Additional X-ray refinement on some crystals of the set gave a better agreement between the SIMS data and calculated site-scattering at Oil (A Oil [%] in the range 0.0-1.4 [%]),where the refinement shows F to be preferentially ordered. This observation seems to provide support, on one hand, to the accuracy of SIMS, and on the other, it confirms the need of extensive study and test (in particular, about the choice of the calibration standards) in the analysis for F by electron microprobe in such complex matrices. 

Fluorine can substitute for OH in many hydrous silicates such as amphiboles, micas, humites, topaz and this substitution has a pronounced effect on the properties auid stability of such phases. Methods for calibrating mineral-gas reactions involving... 

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