ABSTRACT

Dedolomitization is usually a surface phenomenon related to weathering surfaces and hence is commonly found below unconformities. These unconformities may be ancient ones. Recognition of dedolomite in subsurface may suggest a possible unconformity.

Thin sections and stained peels of dedolomite under plane polarized light may reveal a crystalline limestone devoid of ghosts of dolomite rhombs. However, if exactly the same area that has been examined under plane polarized light is viewed under crossed nicols the dolomite ghosts may become evident. These ghosts are diagnostic of dedolomitization.

Peels are normally black under crossed nicols because the acetate is isotropic. Etching may bring out solubility differences between calcite crystals making up the matrix of the dedolomite and those in the original rhombs. During peel preparation, the micron-sized crystals occupying the original rhombs may become attached to the surface of the peel and hence show up as an anisotropic substance demarcating the dolomite rhombs as ghosts. Not all peels of dedolomite show dolomite rhombs under crossed nicols.