no 



CLAYS AND CLAY INDUSTRY. 



meters, and consisting of quartz (Q), mica (M), feldspar (F) 

 and lignite (L), the cloudiness of the feldspar being due to 

 partial kaolinization. Fig. 33 shows the grains of fine and 

 medium sand, and Fig. 34 the clay particles, the former being 

 enlarged 115 diameters, the latter 362 diameters. 



Fig. 31. 



Drawing of an Alloway clay enlarged 362 diameters. 



COLOR. 



An unburned clay owes its color commonly to some iron com- 

 pound or carbonaceous matter, a clay free from either of these 

 being white. Carbonaceous matter will color a clay gray or black, 

 depending on the quantity present, 3 to 4 per cent, being usually 

 sufficient to produce a deep black. A sandy clay will, however, 



