Habit, minerals

The feed preparation stage e.g. by mineral extraetion and evaporation, ehem-ieal reaetion ete. ean give rise to both dissolved and suspended solid impurities, either of whieh may affeet the erystallization step. Removal of suspended solids, e.g. by filtration, is usually the easier proeess. Dissolved impurities ean have by far the more pronouneed effeet, however, and may have to be removed e.g. by ehemieal means or by adsorption. Sueh impurities may, of eourse, aetually be benefieial to the proeess by indueing nueleation, habit modifie-ation ete. 

Postmenopausal women (60-69 y) N=571 Observational Urinary mineral excretion, bone mass Self report No association between calcium excretion or bone mass in abstainers and coffee drinkers with similar smoking habits and degree of obesity. 

Soil is a relatively thin layer of unconsolidated matter on the surface of the earth, in which there is biological activity. The bulk of most soil consists of a mixture of extremely small, loose particles of minerals and organic matter the mineral particles are derived from the weathering of rocks the organic matter from the dead remains of living organisms (Rowell 1994 Limbrey 1975). The composition and texture of the soil are altered by human habitation humans change the natural flora and fauna of entire areas, their activ-... 

Wess, T. J., Alberts, I., Cameron, G., et al. (2002). Small angle X-ray scattering reveals changes of bone mineral habit and size in archaeological samples. Fibre Diffraction... 

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. ... 

When three of the oxygens in the tetrahedra are shared (Si O ratio = 2 5), the complex ions that form take on a sheetlike configuration. The sheets can be stacked, and the associated cations are found between the sheets. Micas and clays are sheet-structure minerals with distinctive habits and physical properties, that reflect the planar silicate sheet structure (Fig. 2.1G). These normally platey minerals may also occur with fibrous-growth habits. The special crystal chemistry that produces such a distinctive habit is discussed later. 

Actinolite-tremolite is another mineral series whose names are well-known because of their fibrous habit. Tremolite, the magnesium end member of the series is depicted in Fig. LIE. Other minerals of similar structure but containing iron as well as magnesium were called actinolite. Ferroactinolite, is the name of the ideal 100% iron (Fe) end member. An accurate designation of the series is... 

Few mineral groups contain as many species, or occur over as wide a range of geological environments, as the amphibole group. The forms and habits... 

Hornblendes, one series of Ca—Al-containing amphiboles (see Table 2.4), are particularly common minerals. Their chemical and physical properties resemble those of the tremolite-actinolite series, but hornblendes generally do not occur in a fibrous habit. They contain Al" in both tetrahedral and octahedral sites, whereas the asbestos varieties of amphibole contain little Al. This observation suggests that small variations in composition may be one of the important factors in generation of fibrous amphiboles. 

The pyroxene group of minerals, where cations substitute one for another at interchain sites, also have a tetrahedral Si site that may contain Al. Some of these substitutions, especially those at M2, can distort the ideal crystal structures, as is depicted in Fig. 2.10. The small distortions are detected as variations in bond lengths between adjacent atoms during crystal structure analyses. These data, combined with accurate composition analyses, could indicate some of the conditions present during growth of the crystal and contribute to our understanding of why some mineral species have formed as fibers. Unfortunately, few detailed crystal structural analyses have been performed on pyroxene minerals with fibrous habits. 

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. 

In his recent book, Dietrich (1985) described the common habits of tourmaline as being acicular, filiform, asbestiform, and chalcedonylike, and as whiskers. This last term indicates that tourmaline composition fibers have been synthesized. The wide range of forms for minerals in this group probably accounts for some of the early confusion when samples of tourmaline were equated with asbestos. Schorl, now known to be NaFe Al6(B03)3Si60ig(0H)4, usually occurs as dark green or black acicular crystals. Based on their appearance alone, schorl could easily be mistaken for an amphibole. 

The members of this group possess a layered-lattice structure, and this is reflected in the platy habit of their crystals and in the perfect cleavage (OOOlj parallel to the layers. The minerals are flexible and soft (2-25). Limited isomorphism is foimd between Mg and Mn. The small number of available analyses, however, influences the record of compositional varia tion in the species. 

Campbell. W. J., E. B. Steel, R. L. Virta, and M. H. Eisner (1979). Relationship of mineral habit to size characteristics for tremolite cleavage fragments and fibers. Bureau of Mines RI. 8357. U.S. Department of the Interior, Report of Investigations. Washington, D.C. 

Amphibole-asbestos A collective term for fibrous varieties of minerals in the am-phibole group. Types of amphibole asbestos are more closely identified (viz an-thopyllite-asbestos). Note that not all members of the amphibole group occur in fibrous form, and those that occasionally do may also be found in other habits (prismatic, columnar, blocky). 

E. 1. Givargizov, Highly Anisotropic Crystals, Dordrecht, D. Reidel, 1986 1. Sunagawa (ed.j. Morphology of Crystals, Parts A and B, Dordrecht, D. Reidel, 1987 1. Sunagawa (ed.). Morphology of Crystals, Part C, Dordrecht, D. Reidel, 1994 1. Rostov and R. 1. Rostov, Crystal Habits of Minerals, Sofia, Professor Martin Drinov Academic Publishing House and Pensoft... 

I. Rostov and R. I. Rostov, Crystal Habits of Minerals, Sofia, Professor Martin Drinov Academic Publishing House and Pensoft, 1999... 

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