Aggregate mineral composition

As noted in Sect. 10.1, heterogeneities play a dominant role in the migration of contaminants in the subsurface. Nonuniform, preferential patterns of flow and transport are ubiquitous. It is important to recognize that, at the field scale, contaminant movement generally is very difficult to anticipate. In natural soils and aquifer materials, macropores, soil cracks and aggregates, fissures, solution channels, root paths, and wormholes, as well as variable mineral composition (e.g., clay aggregates... 

Solid solution theory The chemical theories of primary importance to understanding factors controlling carbonate mineral compositions in natural systems are associated with solid solutions. Carbonate minerals of less than pure composition can be viewed as mixtures of component minerals (e.g., SrCC>3 and CaSC>4 in CaCC>3). If the mixtures are of a simple mechanical type then the free energy of formation of the resulting solid will be directly proportional to the composition of the aggregate. Thus, for a two component, a and b, mixture ... 

Materials Used. The sulfur used was obtained from the refinery and was 99.9% pure. As for the grain form, gravel as spherical material and crushed stone (granulit, basalt) as sharp grain material were used as aggregates. In mineral composition, granulit is an acidic rock, but basalt, on the other hand, consists mainly of basic mineral components. 

In the concrete mix design relatively little attention is paid to the chemical and mineral composition of aggregate. Obvionsly, grading and physical properties, mainly the compressive strength, abrasion resistance, porosity and freeze-thaw resistance are of the highest importance [287,410]. Only in the case of potential risk of alkali... 

The mineral composition of gravel is very complex. The incidental studies of gravel originating from the deposits in northern Poland reveal that this aggregate is of limestone-siliceous type, with various characteristics. The variability of mineral composition of naturally occitrring gravels is clearly visible in Figs. 6.112, 6.113 and 6.114. 

The mineral composition (mode) of the Wyatt Formation in the Scott-Glacier area was determined by Minshew (1967) and is listed in Appendix 6.7.3.1 followed by chemical analyses in Appendix 6.7.3.2. The rocks of the Wyatt Formation in the La Gorce Mountains were altered either by the original magmatic fluid or during later metamorphism. In extreme cases, plagioclase was completely altered to sericite or saussurite (Stump et al. 1986). Saussurite is a mineral aggregate composed of albite and zoisite or epidote with variable amounts of calcite, sericite, and prehnite (Jackson 1997). 

Lithology The character of a rock described in terms of its structure, color, mineral composition, grain size, and arrangement of its component parts all those visible features that in the aggregate impart individuality of the rock lithology is the basis of correlation in coal mines and commonly is reliable over a distance of a few miles. 

FIG. 9—Mineral composition of aggregates in Roman cement cast mortars, showing regionally different types similar holds for in situ run mortars and renders. 

The analytical approach followed two routes. The first was a microscopic study including the use of scanning electron microscopy. By such means, the aggregates were analyzed for their size, shape and mineral composition, and the binder was assessed for its microstiucture, chemical composition, and the mineral composition of relict clinker phases. The second approach was based on the separation of the aggregate from the binder followed by chemical and mineral analysis of the binder and sieve fractioning of the aggregate. 

Calcium siHcate hydrate is not only variable ia composition, but is very poody crystallised, and is generally referred to as calcium siHcate hydrate gel or tobermorite gel because of the coUoidal sizes (<0.1 fiva) of the gel particles. The calcium siHcate hydrates ate layer minerals having many similarities to the limited swelling clay minerals found ia nature. The layers are bonded together by excess lime and iatedayer water to form iadividual gel particles only 2—3 layers thick. Surface forces, and excess lime on the particle surfaces, tend to bond these particles together iato aggregations or stacks of the iadividual particles to form the porous gel stmcture. 

As might be anticipated for minerals with chain structures, pyroxenes commonly occur in columnar, prismatic, rodlike, and acicular forms. Enstatite has been found in the form of rosettes of fine-fibrous crystals. Special names such as victorite, chladnite, and shepardite were assigned to different occurrences in this distinctive morphology, possibly because the fibrous aggregates were located in iron meteorites. However, the composition and crystal... 

These few examples illustrate the range of habits exhibited by minerals whose basic structural units are single chains. In addition, the pyroxenes, which have compositions quite similar to those of the amphiholes, are often found intimately intergrown with the latter double-chain minerals in what appears to be a single large crystal. An intergrowth of amphibole and pyroxene as a fiber, or in a fibrous aggregate, has not yet been described, but it is a likely occurrence. 

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. 

Bauxitic Kaolins andMullites. Deposits of bauxitic kaolins, kaolins having aluminous minerals, have been discovered that have alumina contents between 50 and 70%. These materials are made into refractory aggregates called calcines, grog, clinker, or grain. In addition to sdectivdy mined deposits, synthetic compositions can be prepared from kaolin and alumina and other minerals to produce compositions of desired alumina and mineralogical content. These synthetic mullites are readily available in the form of sintered and fused aggregates. 

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