EXTENDED TO DENSE BODIES. 595 







Theory. 



Abich. 



144Si02 



4320 



65-14 



65-72 \ 



24A1,03 



1248 



18-82 



> from Baveno. 



20KO 



940 



14-17 



1402 r 



4NaO 



124 



1-85 



1-25 ) 



= 8x324 



)6632( 



2-55. 



Expt. 2-5552. 



(See Millar's Mineralogy/, p. 367.) 



Felspar ~n 



On the other hand, the smallest amount of differentiation that is possible on 

 the felspathic, is when we have S instead of K or Na, with only one atom of Li 

 on each of the twelve parts which constitute the compound dodecatom. This 

 gives,— 



Theory. Plattner. 



(-1568102 4680 766 7801 ^ „ ^„ 



Petalite J. 24A1,03 1248 204 18-86 I ^"T , \^- 



( 12LiO 180 2-9 2-76 j I'^^stor.j 



G=8x324 )61U8( 239 Expt. 23-8 . . . 2-4. 



But in all the felspars, the silica greatly overmatches the alumina. Instead 

 of a molecule of silica with an atom of alumina on each pole, the balance of 

 nature is rather the reverse of this, or at least, instead of Ai^)^.JL, it is S AS. 

 Thus, the clay which results from the unremitting application of the atmosphere 

 to the hard compounded rocks, and advances nature towards a vegetable kingdom, 

 has, for its element HSASH = Al2032Si02 + 2HO. We may, therefore, look in 

 nature for some abundant mineral in which the element of the body of the mole- 

 cule, instead of being S merely, shall be SAS. But such a molecule over all 

 its periphery must be wholly non-metallic, like quartz itself. Let us, therefore, 

 differentiate it by introducing more fully metallic matter of the same form. We 

 thus obtain the molecule,— 



KSK (slsX^K SK, 



26Si02 

 Common Mica ^l r2A]203 392 390 ^ from Kimito. 



I 



4K0 



But here small quantities of Fe.fi^, HO, and F, are neglected, and in this 

 region, differentiation is so active, that molecular construction becomes very 

 difficult, and indeed as variable as analyses. 



Stability, simplicity, and facility of construction return, when magnesia and 

 lime are introduced. 



ArragoniteG= (Ca0Cy,„ ^2 8^22 x 20 ^^_^^ ^^p^_ ^.^ _ .^ _ 



^ut as greater stability is urged, or spontaneously acquired, the icosatom must 

 tend to the dodecatom. Hence, a series of structures, giving G = 2-47 to 2-77, of 



