Minerals fibrous

A mineral is a naturally occurring, crystalline inorganic compound with a specific chemical composition and crystal structure. Minerals are commonly named to honor a person, to indicate the geographic area where the mineral was discovered, or to highlight some distinctive chemical, crystallographic, or physical characteristic of the substance. Each mineral sample has some obvious properties color, shape, texture, and perhaps odor or taste. However, to determine the precise composition and crystal structure necessary to accurately identify the species, one or several of the following techniques must be employed optical, x-ray diffraction, transmission electron microscopy and diffraction, and chemical and spectral analyses. 

The long history of bestowing names on minerals has provided some confusing legacies. Many mineral names end with the suffix ite, although not most of the common species no standard naming practice has ever been adopted. Occasionally different names have been applied to samples of the same mineral that differ only in color or shape, but are identical to each other in chemical composition and crystal structure. These names, usually of the common rock-forming minerals, are often encountered and are therefore accepted as synonyms or as varieties of bona fide mineral species. The Fibrous Minerals list (Appendix 1) includes synonyms. 

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.  

---

These fibrous minerals share several properties which qualify them as asbestiform fibers (/) they are found in large clusters which can be easily separated from the host matrix or cleaved into thinner fibers (1) (2) the fibers exhibit high tensile strengths (1) (J) they show high length diameter ratios, from a minimum of 20 up to >1000 (1) (4) they are sufficiendy dexible to be spun and (5) macroscopicaHy, they resemble organic fibers such as cellulose (2). 

The usual definition of asbestos fiber excludes numerous other fibrous minerals which could be qualified as asbestiform following the criteria Hsted above. However, it appears the term asbestos has traditionally been attributed only to those varieties which are commercially exploited (1,2). 

More than 90% of the rocks and minerals found in the earth s crust are silicates, which are essentially ionic Typically the anion has a network covalent structure in which Si044-tetrahedra are bonded to one another in one, two, or three dimensions. The structure shown at the left of Figure 9.15 (p. 243), where the anion is a one-dimensional infinite chain, is typical of fibrous minerals such as diopside, CaSi03 - MgSi03. Asbestos has a related structure in which two chains are linked together to form a double strand. 

Strength Fibrous minerals Ductility gaining tensile strength. Carbon fibers are more expensive fibrous minerals are least expensive but only slightly reinforcing. Reinforcement makes brittle resins tougher and embrittles tough resins. Fibrous minerals are not commonly used in amorphous resins. 

Deflection Temperature (HDT) Fibrous minerals Ductility yield much greater increases in HDT than do amorphous resins. As with tensile strength, fibrous minerals increase HDT only slightly. Fillers do not increase HDT. 

HDT) NA Ductility tensile strength, fibrous minerals increase HDT only slightly. Fillers do not increase HDT. 

Stanton, M.F., Layard, M., Tegeris, A., Miller, E., May, M., Morgan, E. and Smith, A. (1981). Relation of particle dimension to carcinogenicity in amphibole asbestoses and other fibrous minerals. J. Natl Cancer Inst. 67, 965-975. 

Mineral Asbestos Fibers Fibrous mineral silicates... 

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. 

In the remainder of this chapter, specific examples of fibrous minerals are presented. The chemical formulas are given as well as the mineral names. A formula is a shorthand notation that describes the elemental composition of the compound plus the specific ion associations, as determined by three-dimensional structure analysis of the species. Because every mineral sample is not completely analyzed, an ideal formula—one that summarizes the chemistry and associations of the ions—is usually presented. 

Growth of Minerals, Fibrous Minerals, and Synthetic Fibers... 

The most important of these groups is the serpentine mineral group, because it includes the fibrous mineral species chrysotile, which is the most common fibrous mineral and the one most widely mined, processed, and manufactured as asbestos. 

Asbestos is a nonspecific, collective term for a group of fibrous minerals. A sample called asbestos may be composed of one or more of the six minerals listed above and may contain small amounts of other nonfibrous silicate minerals, such as quartz, feldspar, or mica. The definition of asbestos recently published by the American Society for Testing Materials (Ross et al., 1984) can be found in the Glossary. 

---