40 
Proceedings of the JRoi/al Jri.sli Aeade/ni/. 
augite. Gustav Eose"^ found at Mkolajewsk, not far from Miask, 
augite crystals which, when broken, had a nucleus of hornblende. 
The uralite of the same mineralogist is hornblende with an augite 
nucleus. Some crystals, looked upon as uralite, may almost be consi- 
dered as examples of paramorphosis, the angles being those of horn- 
blende, and the cleavage being apparently that of augite, with 
sometimes, as just mentioned, a distinct nucleus of the latter. The 
supposed uralite here spoken of approaches very close in composition 
to ordinary augite. 
Although it is true that many specimens of tremolite may be re- 
presented by the formula Ca"Mg"3Si40i2, and of diopside by the 
formula Ca"Mg'"Si206, and that the proportion of magnesium rela- 
tively to the calcium is greater in hornblende than in many augites, 
the adoption of these formulae, as typical formulae of the respective 
groups, is not admissible, because they exclude the intimate relation- 
ship which the polymeric character of the dyad meta-silicates gives to 
the two groups. Polymerism is indeed so important a link of con- 
nexion, that we may consider all meta-silicates as forming but one 
family, divided into as many groups as there are crystalline series, 
such link of relationship subsists between the condensed ortho or an- 
hydro- silicates. Each member of a condensed series has^a molecule 
differently constituted, and must consequently belong to a different 
crystalline series, as will be evident from the following table, repre- 
senting the general formulae of silicates of dyad metals : — 
Ortho silicates. Meta-silicates. Anhydro-silicates. 
M"2Si O4 . .M" Si O3 1. 
M'sSisOv . .M'aSizOe ..M"Si205 11. 
M"4Si30io . .M"3Si309 ..M"3Si308 . .M" SigO? IIT. 
M'sSiiOia . .M"4Si40i3 ..M'sSiiOu . .M"2Si40io. .M" SiiOg iv. 
M"6Si50i6 . .M'sSisOis ..M'iSisOu . .¥."3815013. .M'^SisOio. .M" SisOu t. 
M'VSieOiQ . .M 'eSisOis . . M^'sSieOn . .M"4Si60i6 . . M"3Si60i5 . . M'-aSieOu . . M"Si60i3, 
M"n + lSi„03» + l .M"nSi„03«. .M"„-iSi,»03n-l. .M„_2Sin03«-2, &C. 
In the ortho-silicates the condensation is effected by successively 
adding the meta-silicate M"Si03 to an ortho-silicate ; or, what is the 
same thing, any condensed ortho-silicate is equal to the simple ortho- 
silicate M'''2Si04, together with the condensed meta-silicate containing 
one atom less. Thus the ortho-silicate M^'eSisOig is equal to M^^SiOi 
+ M''4Si40j2. The anhydro-silicates consist of the meta-silicates, toge- 
ther with one, two, or more molecules of silicic anhydride, according 
as they are more remote from the series of meta-silicates. Thus any 
anhydjo-silicate of series I. may be considered as the meta-silicate 
having the same number of atoms of base plus one molecule of SiOg ; 
any one in series 11. as the meta-silicate having the same number of 
atoms of base^/ws 2 Si O2 ; and so on, an additional atom being added for 
each successive series. The meta-silicate series itself, on the other 
* Reise, ii., 40. 
