A r f lit. Of Regular Stones. 509 
A lump of the TALK-ROCK near Spiral, in the upper 
tafinihia. Given by Dr. Edward Brown. It confifteth of 
broken pieces, like thofe of the Selenites, immerfed in a 
white gloffy Stone, ftained with purplifti fpots, and fo hard 
as to fcratch Glafs. 
Talk, although flexible, and regularly figurd, yet feel- 
eth no Acid and is of that dbftinate nature, as neither to 
melt, nor fcarce loofe its colour, in the fire. Confidering 
which, and that all Salts, yet known, will flow : I am in- 
duced to think, That it hath not ks Figure from any Salt 5 
but is almoft a fimple Earth fui generis. And that there are 
earthy Particles,as well as Saline,-which are regularly figur d, 
and of which this and fome other Stones are compofed. 
Hereof is prepared a wafh for the Face, which fome Chy- 
myfts cry Up for the beft in the World. 
A GREEN TALK-SPAR. The whole piece, is here of 
a rude Figure $ but is eafily broken into Rhomboid Plates, 
refembling thofe of Talk., from whence I have nam'd it. 
9 Tis tinged with a pale Green. It ftirreth not with any 
Acid. Yet is not flexible, as true Talk , but brittle as Glafs. 
A great Cryftalline TALK-SPAR. So I call it. Sent by 
Dr. Erafmus Bart hoi ine, together with a large account of 
it, publilhed in a the Phil. Transactions, (a) And by the 0)Num.£7. 
Dr. (b) himfelf in a diftind: Treatife. 'Tis a foot long, ? a (*) Experi- 
foot broad, and two inches and '* thick. Of a Rhomboid 
Figure , and the narrow fides likewife floaped, as in the « Djf-pi- 
Cryftals of Talk, It breaketh alfo into parts of the fame aclaft,d ' 
Figure, or near it. Yet not flexible, but brittle. Polite, 
colourlefs , and tranfparent, as the cleared Chryftal. Yet 
foft and dinoluble efpecially with Nitrous Spirits 5 and by 
a ftrong fire reduceable to a Calx. Of a very different na- 
ture from Cryftal, although the faid Dr. is pleafed fo to call 
it. When heated, it is of an EleEtrick. Nature, or like Amber, 
taketh up ftraws and other light Bodies. That which he 
principally Notes is, That the Objects feen through it, in 
certain pofitions , appear fometimes fingle , fometimes 
double, and fometimes fixfold. Which he afcribes to a 
Re f ration peculiar to this Stone. And to me, it feems pro- 
bable , That this various Refraction depends upon the 
ftructure of the Stone, fc. as it is not one piece abfolutely 
entire, but compofed of feveral Plates 5 and thofe not all 
