66 ANNUAL REPORT 
Some writers object to the presence of the alkalies, potash and soda 
brought in by the feldspar, claiming that it does not lower the temperature 
of combination (or clinkering) and hence is useless; also that it causes the 
cement to set too rapidly, and again that the free alkalies resulting from 
the decomposition of the feldspar by the lime are liable to cause injurious 
efflorescence. a 
The writer in his experiments has found that these claims are exag- 
gerated. The clinkering temperature was reduced by the addition of even 
small amounts of feldspar and the cements produced were of normal set- 
ting qualities. 
Micaceous Minerals. —These are found in all clays, owing to the 
fact that mica is a mineral resisting atmospheric influences extremely 
well, due to its parallel cleavage. Since the snape of the particles as 
flakes causes them to float readily, we find them invariably associated with 
clay substance, from which they cannot be removed by any washing 
process. But as a rule the amount of micaceous minerals present is not 
great, though they are never absent. 
The principal mica is muscovite, K,03A1,0,6510,2H,O, which we 
find has a strong similarity in composition to feldspar (orthoclase), since 
it contains only two more molecules of alumina than feldspar. We might 
say therefore that it is a somewhat weaker flux than orthoclase. In 
regard to the availability of the combined silica, of course, there can be 
no difference. 
The fusibility of mica has been compared with that of feldspar, both 
being ground very finely and incorporated in a clay body.* It was found 
that 2.308 chemical equivalents of mica exert the same fluxing power 
as one equivalent of feldspar, other things being equal. This fluxing 
ratio is probably still lower for clays which have not undergone extremely 
fine grinding by the wet process, as the flakes of mica are very difficult 
to reduce to impalpable powder, and in the shape of flakes the mineral 
thas no appreciable fluxing influence upon the clay mixture. 
From the chemical standpoint we can safely say that for all practical 
purposes mica may be collected under the heading of feldspathic minerals, 
especially since the amount present is but small, so that really the only 
difference between a feldspathic and a micaceous clay would be a some- 
what higher fusing point. By adopting this assumption the analytical 
work of separating the minerals of a clay is simplified considerably. As 
has already been said, the bulk of the mica is decomposed as readily by 
the action of the calcium oxide at higher temperatures as the feldspar, but 
the reaction is governed much more by the amount of grinding the mica 
has undergone, that is, by the size of the flakes, as the structure makes 
fine disintegration very difficult. 
The Quartz in Clays.—The behavior of quartz in cement mixtures 
hasbeen discussed partlyin other connections. It is found in clays in grains 
*R. T. Stull, ‘‘The Fluxing Power of Mica in Ceramic Bodies,’ Transactions American 
Ceramic Society, Vol. TV, page 225. 
