ABSTRACT

A need exists for concise terminology to describe crystallization textures and fabrics in sedimentary rocks. The rocks which display these textures and fabrics are (a) limestones and dolomites in which the depositional textures and fabrics have been obscured or obliterated, (b) sediments which have formed by crystallization in their environment of deposition, such as evaporites, and (c) chemically deposited cements. To date, no textural and fabric terms have been proposed specifically for these rocks and terms in use have been borrowed from igneous and metamorphic petrology with resultant confusion and inconsistencies. Moreover, in part, confusion is compounded by the chaotic tradition of igneous petrological nomenclature. In this paper, the history and background of var ous terms presently in use have been traced, and a tentative classification is offered to serve as a framework for more extensive textural and fabric analyses. For the size and mutual relations of crystals (crystallization fabrics), the terms xenotopic, hypidiotopic, and idiotopic describe both equigranular and inequigranular fabrics, and the terms porphyrotopic and poikilotopic describe inequigranular fabrics. For the shape of mineral crystals (crystallization textures), the igneous terms of the C.I.P.W. system (anhedral, subhedral, euhedral), which are already widely used by North American carbonate petrologists, are recommended for more extensive usage.

Idiotopic dolomite commonly has porosity and makes a good reservoir rock for oil and gas. Hypidiotopic dolomite may or may not be porous, and xenotopic dolomite normally has little or no porosity.