Ceramic clays and shales of Ontario

Abstract

Forty-nine representative samples of Ontario clays and shales, mostly from well populated areas, were investigated by X-ray diffraction, differential thermal analysis, drying and firing techniques, and chemical analysis. With the exception of the kaolinitic Cretaceous clays of the Missinaibi valley of northern Ontario, all samples were found to be low-fusion, heterogeneous materials. The shales have the most favourable properties for brick making, whereas many of the surface clays are suitable only for the manufacture of partition and drain tile. Nine typical samples were selected for special study by plastography, thermogravimetry, dilatometry, and temperature -gradient firing. Processing problems, such as short firing ranges, heating and cooling cracks and kiln atmosphere, are discussed in relation to mineralogical composition. The mineralogical investigation revealed that the Palaeozoic shale samples of Ontario contained a clay mineral suite consisting essentially of illite and chlorite. Common non-clay shale constituents included quartz, carbonates, and plagioclase. A study of the differences between clay mineral suites derived from the Canadian Shield and the Palaeozoic sedimentary rocks led to the discovery of mineralogical criteria whereby the origin of the clay minerals within individual Pleistocene clay deposits could be recognized. Clays containing the Palaeozoic clay mineral suite occurred throughout southern Ontario west of Toronto. Weathering alteration of these usually resulted in the formation of "frayed edge" clay mineral structures which often consisted of multicomponent mixed-layer systems. In several instances both chlorite and illite were thus affected, although the alteration of the more labile trioctahedral chlorite was generally greater. The Shield-derived clays contained highly varied, structurally disordered, clay mineral assemblages which were invariably rich in expandable phases, some of which occurred as unmixed minerals. A characteristic suite of non-clay constituents, rich in plagioclase, amphibole and K-feldspar, was also associated with the Shield-derived material.