190 Dr. Thomson’s Notice of some new Minerals. 
the lustre is vitreous and the texture imperfectly foliated : its 
hardness is only 3°75, which is a good deal less than that of 
felspar. Its specific gravity is 2°568. 
Before the blowpipe it becomes white but does not melt. 
With carbonate of soda it melts into a green coloured bead, 
and on adding nitre the colour becomes red: with borax it 
fuses into a colourless bead. 
Its constituents were found to be 
PNINOR a, i} a stam le aneEh teteue tes, 1 diate 
Ws 0 Le Ry A ge PR SR Rey 7°60 
OLAS Ese amet etal et a ota ee 
DIE ns thane deta, den a teiane ait PDO 
Maonesia‘., isin» daiacas,» of s00 
Oxides of iron and manganese 1°25 
VEGIBLUILD ae nrg, hss, alisheum eel eal 
99911 
The silica is much greater than in felspar, and the alumina 
much less, while the proportion of potash is nearly the same. 
If we were to consider the lime and magnesia and the oxides 
of iron and manganese as accidental bodies united to silica in 
the same ratio as the alumina and the potash, the constitution 
of the mineral might be represented by 4(A1S°) + 3 (K $°). 
If the lime and magnesia be essential constituents, the formula 
will be Al S°+(&K+4Cal+3 Mg) S. 
4. Silicite-—TVhe fourth mineral which I shall notice I have 
distinguished by the name of Silicite,from the great resemblance 
which it has to quartz in its external aspect, though it differs 
entirely from that mineral in its constitution. It occurs in 
a basaltic rock in the county of Antrim, and was given me by 
Mr. Doran, an Irish mineral dealer. 
The colour is white with a shade of yellow, the texture fo- 
liated, and the fracture small conchoidal. Its lustre is vitreous, 
its hardness nearly the same as that of quartz, and its specific 
gravity 2°666, or nearly the same as that of rock crystal. 
With carbonate of soda it fuses into an opake bead, and with 
borax into a transparent colourless bead. Its constituents are 
3) 4 UL or etna btu tebe act te Yr 5 Ys) hay 
PATUMIINe se ele an eo eek 
Protoxide ofiron .... 40 
Ley tials yee i eager La terry mespanted [ofeat 
byt) eda lis East 7 O64 
100°24 
If we suppose the oxide of iron to be combined with alu- 
mina and to be only accidentally present, the constitution of 
silicite will be 7(AlS*) + 2(Cal 8), 
