370 Dr. Odliug on Ortho- and Meta-silicates. 



and carbonate of lithium, Colonel Yorke obtained an ortbo- 

 silicate of lithium, Li'* SiO'*; with silica and carbonate of potas- 

 sium, a metasilicate of potassium, K^ SiO^ ; and with silica and 

 carbonate of sodium, an intermediate | silicate of sodium, 

 Na" Si2 0^ or (Na* SiO" . Na^ SiO^). And it will be found that 

 all non-aluminous silicates which do not contain an excess of 

 silicic anhydride, may be referred to one or other of the three 

 types,— M4 SiO" Orthosilicate = 2W . SiO^. 



M^SiO^ Metasilicate = M^O. SiO^. 



M« Si07 f Silicate = SM^ O . 2810^. 

 If we consider alumina as always basic, then there are silicates 

 in which the basicity exceeds that of the tetrabasic group ; but 

 the basic or acidulous function of alumina in many minerals is 

 yet subjiuKce; and if we exclude aluminous minerals, we shall 

 find that the tetrabasic are the most highly basic of all known 

 silicates, natural or artificial. As illustrating the existence of 

 the above three classes of silicates, I append the following lists, 

 which are capable of considerable extension. It is observable, 

 however, that the orthosilicates are far more numei'ous than 

 either the meta- or | silicates, — that they are, in fact, the normal 

 salts, both as regards constitution and distribution. 



Class I. Orthosilicates. 

 Type 1\I'* Si 0^ coiTesponding to M^ PO-* orthophosphate. 



Et^ Si 0" Silicic ether (2 vols.). 



Li'' Si O'* Orthosilicate of lithium (Yorke). 



Na'* Si O'* Orthosilicate of sodium (Yorke). 



Ca^SiO"* Orthosilicate of calcium (Sefstrom). 



Mg^SiO^ Olivine; chrysolite. 



Ca^Mg2 Si O-* Batrachite. 

 Zn-i Si O"* . H^ Zinc glance. 



Gl'' Si O-* Phenakite. ' 



Y'*SiO'* Gadolinite. 



Ce4 Si 0^ Cerite. 



zr"" Si 0'» Zircon. 



Mu"* Si 0"* Orthosilicate of manganese. 



Mn2 012 Si 0" Helvine. 



Fe'* Si O"* Fayelite ; forge-cinder. 



(]\IgFe)4Si04 Hyalosiderite. 



Fe^ Mn^ Si 0* Knebelite. 



/e^ Si 0* Yellow earth (Kuhu). 



r/eFeCa)'*SiO* Ilvaite. 



Cu2 H^ Si 0" Dioptase. 



flZ-* Si 0"* Bucholzite. 



fl^^Ca^SiO** Garnet; idocrase ; vesuvian. 



aF Ca Si 0"* Wernerite ; anorthite. 



aP (CaNa) ' Si O"' Thomsonite. 



aP Mn Si O"* Karpholite. 



