188 Dr.Thomson’s Notice of some new Minerals. 
pendent, so that equations may be framed that shall satisfy 
them all. 
We cannot infer therefore that there are always as many 
pairs of imaginary roots as there are conditions fulfilled, al- 
though it is probable that there does exist a connexion be- 
tween the number of conditions and the number of imaginary 
pairs. But this is a matter that requires further investigation. 
Belfast, Jan. 13,1843. [Tc be continued. ] 
XXX. Notice of some new Minerals. By Tuomas THom- 
son, M.D., F.RS. L. 5 E., M.R.LA., §c., Regius Pro- 
fessor of Chemistry in the University of Glasgow. 
NE of the most abundant and important minerals is fel- 
spar, which constitutes the principal constituent in gra- 
nite and gneiss, and together with hornblende forms the rocks 
so prevalent in this part of Scotland, I mean greenstone and 
basalt. Felspar is a double salt, being composed of 3 atoms 
of tersilicate of alumina and 1 atom of tersilicate of potash. 
Sometimes the potash is replaced by soda. ‘The mineral in 
that case is distinguished by the name of albzte, and differs in 
the shape of its crystals; three of the minerals which I mean 
to notice at present are connected with felspar, though they 
differ from it in their composition. 
1. Erythrite—The first species which I shall mention is 
erythrite. It occurs rather abundantly in the Kilpatrick 
hills, and also in the amygdaloid on the south side of the 
Clyde near Bishoptown. I do not know who first noticed it, 
but it was brought to me some years ago as a new mineral 
by Mr. Clackers, a mineral dealer in Old Kilpatrick. I call 
it erythrite, on account of the flesh-red colour which distin- 
ouishes all the specimens which I have seen. 
Its specific gravity is about 2°541, which agrees with that 
of common felspar. And its hardness is about the same as 
that of felspar; the texture is compact, or at least not sensi- 
bly foliated, and I have never seen a specimen of it in crystals. 
It is composed of 
Silica. 26 oS ee STE, 167190 
SATs vies Sete ihe oe 11800 
Peroxide of iron. .... 2°70 
ETI wi Het Sercwere Hed set raps 1:00 
Magnesia’... 0.26 3°25 
Mefgent es Pe. sO 
ip ne er 1:00 
101°35 
* Read before the Glasgow Philosophical Society, 2nd of November 
1842, and now communicated by the Author. 
