Classification of Dolomite Rock Textures

ABSTRACT Dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape. The classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics, and crystal boundary shape is controlled by growth kinetics. Size distributions are classified as unimodal or polymodal. Crystal boundary shapes are classified as planar or nonplanar. If the evidence permits, a complete classification includes a description of recognizable allochems, matrix, and void filling. Allochems and preexisting cements may be unreplaced, partially replaced, replaced mimically, or replaced nonmimically. Allochems may be dissolved, leaving molds. Matrix can be unreplace, partially replaced, or replaced by a unimodal or polymodal size dolomite. Unimodal size distributions generally indicated a single nucleation event on a unimodal substrate. Polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate. Planar crystal boundaries develop when crystals undergo faceted growth, and nonplanar boundaries develop when crystals undergo nonfaceted growth. Nonplanar boundaries are characteristic of growth at elevated temperature (> 50°C) and/or high supersaturation. Both planar and nonplanar dolomite can form as a cement, replacement of CaCO3, or neomorphism of a precursor dolomite.