7 Messrs. Johnson and Blake on Kaolinite and Pholerite. 357 
and in this position they have the greatest effect aber polarized 
_ light. They have least influence on the polarized beam when 
the plane of polarization is perpendicular or parallel to the plates 
in this position. The separate plates are of broken and irregular 
outline. Grains of quartz are intermingled. 
In four other specimens of kaolin from unknown (probabl 
European) localities, similar prismatic bundles were observed. 
The bundles were usually curved and irregular; in some in- 
stances their length was four or five times their breadth. One 
of these four kaolins contained hexagonal plates that could be 
made out with ease under a one-fourth inch objective. Two 
others, when rubbed between the fingers, assumed a distinct 
pearly luster; and after this treatment, by which the prismatic 
crystals were broken up, microscopic examination revealed 
Prof. Brush has called our attention to a specimen of fluor 
from Zinnwald on which occurs a white powdery substance 
that passes for kaolin. It consists entirely of perfectly definite 
hexagonal tables averaging ‘0005 of an inch in diameter, which 
are usually thin but sometimes are aggregated into short prisms. 
The kaolin, pseudomorphous after prosopite, from Altenberg, 
Saxony, the analysis of which by Richter (Pogg., xc, 315) is 
given below, though compact in texture, is found by microscopic 
examination to be made up also of hexagonal plates and bun- 
dles of plates. 
when rubbed between the fingers they | e more soapy to 
he feel. So too the crystallized kaolinite accompanying fluor 
from Zinnwald is a scarcely coherent unplastic substance. 
e more finely divided fire-clay from Long Island, is more _ 
“fat,” while the Bodenmais porcelain earth and other clays, in 
which the bundles are absent and the plates are extremely small 
are highly plastic. So, too, the Summit Hill crystals, when tritu- 
in an agate mortar, yield a powder which, when breathed 
upon, acquires the argillaceous odor, under the microscope pé 
fectly resembles the finer kaolins, and in the wet state is high 
plastic and sticky. oe 
Sommaruga has published analyses of two Passau kaolin 
_ Aw. Jour. Sc1.—Szconp Serres, Vou. XLIII, No. 129.—Mar, 1867. 
: 46 
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