Mineralogy, chemical system

The following pages give a review of the chemistry of natural minerals, their typical occurrence in nature and their common mineral associations. This review is used to establish the major groupings of the common clay mineral species as a function of the chemical systems to which they can be related. Because various forms of silica as well as zeolites and organic materials are commonly associated with clays, these materials have been considered in the same manner as the phyllosilicates. It is evident that they have an influence on the clay mineralogy and that they form an integral part of clays in the broad sense of the term. However, they are not normally considered to be clay minerals. 

Simple empirical relationships between fusion temperature of the furnace deposits and the mineralogy of coals have been proposed (4,5,6). More recently attempts have concentrated on a physicochemical view of the problem comparing ash fusion temperatures with phase relations in three-component chemical systems (7,8). This method of attack has yielded some significant results, but at least some researchers (8) have questioned this approach, which is based... 

Some of the differences are no doubt related to the con5)lexity of the mercury system including the various forms of mercury produced under varying environmental conditions and also on the lack of laboratory and field control, particularly in relation to detailed and accurate characterization of sediments. Sorption phenomena are strongly dependent on the t5q>e (mineralogy, chemical species, etc.) and also on the total available surface area of adsorbing materials. These variables must be accurately determined if reproducible results are to be found in any mercury sorption study. 

In 1820 Berzelius wrote Cronstedt, the founder of the chemical system of mineralogy, a man who by his acuteness in that science rose so far above his age that he was never correctly understood by it, used the blowpipe to distinguish between minerals . 

The uniformity in this distribution is surprising. Most rocks are heterogeneous, complex chemical systems with complicated histories. There was no reason to presume that two samples of rock from the same rock formation, or even adjacent fragments from a single sample would show such similar lanthanide distributions, let alone rocks of different ages, from different places, and with different bulk compositions and mineralogies ... 

Helgeson, H. C., 1970, A chemical and thermodynamic model of ore deposition in hydrothermal systems. Mineralogical Society of America Special Paper 3, 155-186. 

Most minerals occur in a variety of morphologies. Although it is not exhaustive, the list we recorded as occurring in fibrous form (Appendix 1) contains more than 350 entries, each with a reference. The format follows that proposed in Dana s System of Mineralogy, (Palache, et al., 1944), one of the standard references in the field. The names of fibrous minerals are alphabetically arranged within each chemical group that is, elements, oxides, hydroxides, carbonates, sulfates, phosphates, and so on. A similar, parallel system has been adopted for the list of synthetic fibers (Appendix 2). The list of synthetics includes glassy fibers produced from natural materials, as well as whiskers. 

A formal description of a mineral presents all the physical and chemical properties of the species. In particular, distinctive attributes that might facilitate identification are noted, and usually a chemical analysis of the first or type specimen on which the name was originally bestowed is included. As an example, the complete description of the mineral brucite (Mg(OH)2), as it appears in Dana s System of Mineralogy, is presented as Appendix 3. Note the complexity of this chemically simple species and the range of information available. In the section on Habit (meaning shape or morphology) both acicular and fibrous forms are noted. The fibrous variety, which has the same composition as brucite, is commonly encountered (see Fig. I.ID) and is known by a separate name, nemalite. ... 

From every chemical group mentioned in Dana s System of Mineralogy there are minerals that form as fibers. We began with the most commonly encountered minerals, the silicate and aluminosilicate groups, and now briefly mention a few from other chemical classes. 

This indicates that a general geothermal pattern has been established in the total column and that rapidly circulating warmer water has only local effects on the clay mineralogy. The mineralogy of these different types of semi-permeable rocks corresponds, on a depth-temperature basis, very closely with that found in pelitic shale rocks of other studies. It is likely therefore that high permeability gives a noticeably different set of chemical parameters (intensive variables) to a rock whereas medium to low permeability can be assimilated to a "closed" system where rock and fluid are effectively part of the same physicochemical unit. 

It is important to note two things in this analysis first, the reactions which govern silicate phase equilibria occur in a system closed to large-scale chemical migration. This corresponds to a pore-water sediment system of local equilibrium. Second, the most striking mineralogical change—the crystallization of feldspar—is, in fact, the result of the instability of another phase, montmorillonite. The use of... 

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