The composition and properties of ceramic clays and shales of Quebec

Abstract

Forty-one representative samples of clays and shales were investigated by various firing methods and by X-ray diffraction, differential thermal analysis and chemical analysis. In addition, thirteen of the samples were studied by thermogravimetric analysis, thermal expansion and plabticity measurements, to determine their processing problems. The results show that, with the exception of some refractory kaolinrich samples occurring on the Canadian. Shield which have a white to brown fired colour, the ceramic clays and shales of Quebec are common, heterogeneous, mainly red-firing materials. Most of the clays are suitable only for making common brick and tile because they have short firing ranges and high fired shrinkages at temperatures where they become dense and very hard. As a rule the shales are more suitable than the clays for making dense facing brick, because they usually have longer firing ranges. The Quebec Group shales are more refractory and usually have more plasticity and fewer processing problems than the Utica, Lorraine, Rockcliffe and Queenston shales of the St. Lawrence Lowlands. Some of the Quebec Group shales are probably suitable for the manufacture of sewer pipe. The majority of the kaolin-rich samples, as they occur, are not suitable for ceramic products; many are contaminated with minerals containing iron. The principal clay minerals in the common clays and shales are illite and/or chlorite. The majority of these samples contain mixed layer systems involving combinations of illite, and/or chlorite, with an expandable phase. Kaolin is a principal component of the kaolin-rich samples only. The principal non-clay minerals are quartz, feldspar, calcite, dolomite and pyrite. The principal constituents in thirteen fired specimens are quartz and feldspar with lesser amounts of cristobalite, mullite, hematite and rutile.