OF CORNWALL. 
XI 7 
CHAP. XI. 
Of the general bafis of Stone , viz. Of Spar, Cryftal , and Diamond. 
T HERE is a kind of ftony lapidific matter which runs 
through and mixes more or lefs with the fubftance of all 
ftones, and may juftly be efteemed the univerfal cement, by which 
earth and minerals are combined into all the fevejal orders and Ipe- 
cies of ftones, for when this cement is diflipated by fire, or diftol- 
ved by a menflruum , the ftone becomes earth or metal ; and ceafes 
to be ftone : it is of itfelf tranlparent and colourlefs, but when 
mixed, is found either of that colour which the materials it joins 
together were of before they became ftone, or of that which any 
after infection from other bodies has imparted. 
This cement is either lpar, cryftal, or diamond. Thefe I fball not 
only treat of as being diftincft ftones, in figure, nature, and effedt, but 
as one univerfal cement, running through and connecting all other 
ftones in three degrees of purity and perfection. Thus for inftance 
lpar not only forms fimple ftones of its kind fuch as the Lapis fpecu- 
laris , double rcfradting and fimple refradting fpar, ftaladtites and the 
like, but is indeed the bafis of a great number of compound ftones, 
from the tendered: lithophytes to thehardeft marbles. So again, cryftal 
not only forms hexagonal columns, and cufpides, pyramids, and the 
like, but is the gluten, the connecting bafis of flat, killas, granite, flint, 
porphyry, and the like ; as diamond is allb the bafe of gems. The 
ftate of fpar is the moft impure, its parts are calcarious, lax, dif- 
perfed, they ferment and give way to acids, are extracted, fufpended, 
and walked away by common water, confequently the ftones which 
it combines are foft, brittle, and eafily diflolved ; .this is the cafe of 
all ftalactical productions, of alabafter, free-ftones, lime-ftones, and 
moft forts of marbles, of which the cement is fpar. But the 
cement of fpar is not always equally weak, lometimes it will fcarce 
ferment at all, gives fire with fteel b , and it approaches fo near 
the ftate of cryftal, in hardnefs, tranfparency, and figure, that it 
is juftly called cryftalline fpar. 
Cryftal has nothing calcarious in it, it’s parts unite clofe and 
firmly, and confequently forms much harder ftones than lpar, with 
equal quantity of earth, fand, or whatever the charge or materials 
in grofs may confift of, and this is the cafe of porphyry, granite, 
jalper, and other compound ftones, (whofe bafis is cryftal) as well 
k See the Spatum compaflum fcintillans Linrusi Syjl. Hat. gen. vi. page 167. 
H h 
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