Feldspar

 Most of the world's feldspar is used in glass-making and in the production of ceramics such as wall and floor tiles and sanitaryware. It is also used to produce glazes and enamels and electrical porcelain. Feldspar occurs mostly as white, green or red-brown, ranging from flesh colour to the colour of brick. A special type of feldspar is extracted from pegmatites in very small quantities (50-100 t per year) at a mine near Buckingham, Québec. This feldspar has a glassy lustre, is high in potassium oxide (K2O), and low in sodium oxide (Na2O) and iron oxide. All production is exported in lump form (4-7 cm), mainly to the US, where it is transformed into dental porcelain powders. To process feldspar, it is cleaned manually of its mica and quartz nodule impurities. It is crushed and then cleaned of its iron impurities with a magnetic separator. Pure feldspar is mixed with glass powders and metal oxides and fired in electric ovens. The resulting product is ground fine, mixed with pigments, screened to different sizes and blended. The powders are then baked to produce dental porcelain of different translucency, colour and shades.