MINERALOGY. 
tin calx might by itfelf take a fpherical polygo^ial 
figure^ at its inderatio fi,, as well as. the garnet. 
The white' tin grains,. (Se£l. ccx*) out of 'which 
BO tin,, but only iron, is to. be got, might widi 
more reafon be placed here, if it was not fo ex-- 
ceirively refrafbory in the fire, and if it. did 
fiot, at laft, melted either by itfelf, or ¥nth borax, 
give a clear and colourlefs. glafs., contrary to what 
the garnet does, wkkh difference arifes Irom the 
different fofibility of thefe two fubftances. 
The garnet and cockle are not yet known to 
me in form, of m earth or clay, taken in the 
common idea we have of tliofe bodies.. It is 
true, that there is a bole found at Swappawari, 
in Lapland, which has the fame figure as the gar** 
net^ and the hornblende, (Sedr,.. lxxx.¥iii.) wEeh. 
is fomewhat harder than this bole, -has often, the' 
appearance of a cockle. Yf e cannot, however, do 
more than probkniatically fupprfe them: to he 
the neareft related to the garnet kind, as 'we have 
not yet difeovered a method how to lepam.te 
earths from the contained metals, v/ithout ie- 
Itroying their natm^al form, and efpecially from 
iron, when it is fa ffmngly united vdth them^ as 
if it had a part in tlieir formation itfelfi 
SECT. LXXYIL 
The Fourth Order. 
The Argillaceous Kind, Argillace^. 
The principal character whereby thefe may 
be diftinguifhed from other earths, is, that they 
harden in the fire, and are compounded of very 
minute particles, by which they receive a dead or 
dull appearance when broken.. 
