jmineralogt; % 
which it fo nearly refembles, that it is notf 
eafy to point out fuch characters as fhall rea- 
dily diftinguifti it from them. The bell 
way, perhaps, will be to fpeak of its pro- 
perties comparatively 5 and then we may fay 
that, 
1. It is more uniformly folid, and not fo 
much cracked in the maft as the quartz i 
and, 
2. It is more pellucid than the jafper. 
3. It bears being expofed to.the air, without 
decaying, better than the jafper, but not 
fo well as the quartz. 
4. It is better for making of glals than the 
jafper, but is not quite fo good as quartz 
for that purpofe. 
When ever there has been an opportu- 
nity in this matter of its fhooting into 
criftals, quartz crifcals are always found 
' in it ^ juft as if the quartz had made one 
of its conflituent parts, and had on cer- 
tain circumitances been fqueezed out of 
it ; this is to be feen in every hollow 
flint, and its clefts, which are always filled 
up with quartz, 
6. It often fhews moft evident marks of 
having been originally in a foft and filmy 
ftate. 
The feveral varieties of this fpecies 
have obtained diftincl names, more with 
refped to their colours, than from any 
real difference in their fubilance ; but 
tliefe are ftill neceffary to be retained, as 
the only names ufed by jewellers and 
others, who know how to value them ac- 
cordingly. 
SECT, 
