MINERALOGY, 201/ 
This is of a whitifli yellow colour, 
contains likewife a great deal of iron, 
and has the fame quality with the for- 
mer, to harden foon in water, when 
mixed with mortar. This quality can- 
not be owing to the iron alone, but 
rather to fome particular modification 
of it, occafioned by fome accidental 
caufes, becaufe thefe varieties rarely 
happen at any other places, except 
where volcanos have been, or are yet 
in the neighbourhood* 
SECT. CCX. 
Calx of iron, united with another un- 
known earth, Ferrum calciforme terra 
quddam incognita intime mixtum. The 
T ungfien of the Swedes. 
This is alfo, though improperly, called 
White Tingrains. Sed. clxxxi. 
This refembles the garnet-ftone, 
(Se6l. Ixix.) and the tin-grains ^ is nearly 
as heavy as pure tin ; very refraftory in 
the fire, and exceffively difficult to re- 
duce to metal. Iron has, however, been 
melted out of it to more than 30 per 
cent. It is very difficultly difiblved by 
borax and alcaline falts, but melts very 
eafliy with the microcofmic fait, giving 
a black flag : And for this reafon, this 
lafl: mentioned fait mufl: be employed in 
the experiments on this flone. It is 
found, 
I Solid and fine-grained. 
a, Reddifh or flefli' coloured, 
h. Yellow. 
