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The basis of their use and definition is given below

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impractical and both terms have been retained and defined as recommended terms. The basis of their use and definition is given below. Cleavage is the property of a rock to split on a set of regular parallel or subparallel planes. Cleavage was the subject of extensive study and discussion among early structural geologists and its classification was largely based on the assumed mechanism of its formation (see review in Wilson, 1961). This led to a great confusion of terms. In order to address this problem, Powell (1979) proposed a systematic classification based on morphological rather than genetic criteria. Powell’s scheme forms the basis of current definitions and is largely adopted here. Powell divided cleavage into continuous cleavage and spaced cleavage. Continuous cleavage is present throughout the rock at the grain-size scale and may be subdivided into fine continuous cleavage as found in fine-grained rocks, and coarse continuous cleavage as found in coarse-grained rocks. Spaced cleavage is subdivided into crenulation cleavage and disjunctive cleavage. The latter is developed independently of any pre-existing mineral orientation in the rock (e.g. fracture cleavage, pressure solution cleavage). (See below for full definitions of these terms.) Schistosity is the preferred orientation of inequant minerals in a rock . Schistosity, in some form, is present in most cleavage types. Only in certain disjunctive cleavages (e.g. fracture cleavage) is schistosity absent. Well-developed schistosity is characteristic of continuous cleavage and is independent of grain size . Thus, at the simplest level, all rocks with such a structure may be termed schists. However, it is common practice to refer to fine continuous cleavage as slaty cleavage and the associated rocks as slates. www.bgs.ac.uk/scmr/home.html
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KHB Page 5 1/29/2007Paper_3.doc 2B Foliation 3B Foliated structure was used by Macculloch (1821) to denote a coarse mineral layering with a poor splitting: the equivalent, in modern terms, of gneissose structure. Darwin (1846) defined foliation and gave it the same meaning. This usage and meaning became established, particularly in British petrological literature (e.g. Harker, 1939; Fairbairn, 1948; see review in Wilson, 1961). In American literature, however, the term was generally taken to include schistosity and cleavage (e.g. Knopf & Ingerson, 1938; Turner & Weiss, 1963). This latter, wider meaning, is now prevalent (e.g. Spry, 1969; Tomkeieff, 1983; Park, 1983; Barker 1990; Davis & Reynolds, 1996) and is the one adopted by the SCMR. In this sense it is equivalent to s-surface (Turner & Weiss, 1963, p.97). 6B Structure, texture and fabric The use of the terms structure, texture and fabric may give rise to ambiguity. This is particularly true when the same words in other languages may have different meanings. Structure
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