Sinter Aggregates of Minerals

mineral masses that form primarily through the precipitation of carbonate, sulfate, phosphate, and other chemical compounds from surface or hydrothermal solutions. Sinter aggregates may form from colloidal solutions (called collomorphic aggregates), and also from true solutions, by a special mechanism of generation and rapid growth of microcrystals.

Sinter aggregates appear in the shape of icicles (stalactites and stalagmites), knobs, nodular crusts, and irregular incrustations with typical concentric-zonal or radial structure. The waters circulating in the earth’s crust and on its surface dissolve significant quantities of numerous minerals, especially carbonates of the alkaline earths. Exchange reactions or evaporation of water and a change in temperature and pressure conditions lead to the separation of dissolved substances in the form of sinter aggregates of minerals. Sinter aggregates form on the earth’s surface and in the surface layers of the crust: in deposits of geysers and mineral springs, in caves, in cracks and cavities within rocks, in zones of oxidation of ore deposits, and in old mines. However, collomorphic aggregates of ore minerals (such as pyrite, sphalerite, and cassiterite), also form from deep hydrothermal solutions. The most common sinter aggregates are those of calcite, aragonite, malachite, brown hematite, copper phosphatites, copper sulfate, and chalcedony.