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Foliation index determination for fine-grained metamorphic rocks

Détermination d'un indice de foliation dans les roches métamorophiques à grain fin


The fine grain size of rocks such as slates, phyllites and hornfelses limits the accurate determinations of their foliation index values using the optical microscope. An experimental study has therefore been undertaken for a more relevant approach to evaluating the index. X-ray diffractometry on rock specimens at extreme orientations is ideal.

The rock types studied fit well into a proposed classification scheme. This reaffirms that foliation index is a reliable parameter for the quantitative fabric characterization of metamorphic rocks which bears a practical significance to their engineering performance.


La finesse des grains de roches telles que les schistes, phyllades ou cornéenes empêche une bonne dêtermination de laur indices de foliation au moyen du microscope optique. Une étude expérimentale a donc été entreprise pou trouver une meilleure approche de cet indice. L'idéal est la diffractométie RX effectuée sur des échanitilloons de roches parfaitement orientés.

Les roches étudiées trouvent ensuite place dans une classification, ce qui prouve une nouvele fois que l'indice de foliation est un paramétre fiable pour caractériser quantitativement la structure des roches métamorphiques, qui a elle-même une influence déterminante sur leur comportement mécanique.

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Tsidzi, K.E.N. Foliation index determination for fine-grained metamorphic rocks. Bulletin of the International Association of Engineering Geology 36, 81–88 (1987).

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  • Chlorite
  • Prefer Orientation
  • Metamorphic Rock
  • Shape Factor
  • Hand Specimen