Constitution of the Natural Silicates. 453 



for three days, gave 51*08 per cent of insoluble residue. From 

 this, soda solution extracted 21*54 of silica, leaving 29 - 54 per 

 cent of an undecomposed silicate. This, analyzed independ- 

 ently, contained 



Si0 2 45-08 



Al o 3 22-82 



Fe" 2 3 10-01 



MgO 21-48 



99-39. 



Hence the ratios Si0 2 : R 2 Q 8 : MgO = 75 : 29 :54 ; which corre- 

 spond nearly to a mixture of Al 2 Si0 5 with Mg 2 Si 2 6 . As to 

 the real nature of this residue, we can only offer the foregoing 

 suggestion as a plausibility. Positive knowledge is lacking. 

 The vermiculites, however, are alteration derivatives of the 

 micas ; and. by their metamorphosis kyanite, tibrolite, or anda- 

 lusite may be generated naturally. Geologically, the sugges- 

 tion is worthy of consideration. 



Now, from the two analyses we get the subjoined molecular 

 ratios. 



Jefferisite. Kerrite. 



Si0 2 ... -5V0 -635 



R 2 3 -209 -124 



RO - -526 -694 



H 0, over H 2 S0 4 -587 -5-24 



H 2 0, 250°-300° -233 -226 



H 2 0, constitutional -355 '363 



Hence the empirical formulae 



Jefferisite R'" tt R" H H 70 Si„O„. + 82H 2 



Kerrite R"' M R"_ M H J3i M 0,„ + 76H.O 



From the jefferisite gaseous hydrochloric acid removed 10 

 atoms of magnesia, and from the kerrite 8 atoms. Taking 

 this, hypothetically, as MgOH, we have 



Jefferisite .... R"' tt R" tt (MgOH) 10 HJSiO J 5T 0„ + 82H 2 

 Kerrite R'" 14 R". l (MgOH) 8 H at (Si0 4 ) M T + 76H.O 



H The small excess of oxygen in these expressions needs to be 

 accounted for. To regard it as forming the group AlO, how- 

 ever, is impracticable ; for then the residual aluminum atoms 

 would be less than one-third the silicic groups, which is inad- 

 missible under the mica theory. The simplest interpretation 

 is as follows : In the clintonite group the general formula 



R m/ >R" 



x SiO=R' 3 



seems to apply. If we treat the excess of oxygen in the two 

 vermiculites as pertaining to molecules of this order, the com- 



