MINEEALOGY; WJTH A CLASSIFICATION OF SILICATES. 



73 



give its geometric form to a large portion of some extraneous matter, which it compels, as 

 it were, to assume its own crystalline shape. 



Tribe 13. — Peradamantoid. 



§ 95. It may be noticed that in the second suborder the less protobasic silicates do not 

 assume zeolitoid or spathoid forms. With the exception of sloanite and forestite (both of 

 which demand further study) we find no species in these tribes having a ratio of protoxyds 

 to sesquioxyds greater than 1 : 4 ; those presenting the higher ratios, up to 1 : 12, being 

 adamautoids, phylloids and j)initoids, through which this suborder is connected with that 

 of the persilicates. As might be expected, we find these conditions continued in the latter 

 suborder, in wliicli all the species known are, with one exception, included in the cor- 

 responding tribes. These are designated, as we have seen, peradamantoid, perphylloid 

 and argilloid, wliicli latter represents the piuitoid and ophitoid tribes of the preceding 

 suborders. The single exception as yet known is the westanite, described by Blomstrand, 



XII. 



Tribe 13. Peuadamantoid. 



Species. 



Dumortierite. 



Andalusite. - - 



Fibrolite. - - - 



Topaz. - - - - 



Cyanite. - - - 



Bucholzite. - - 



Xenolite. - - - 



Worthite. - - - 



Lyncurite. - - 



Malacone. - - - 



Zircon. - - - - 



Auerbacbite. - - 



Anthosiderite. - 



Formula. 



(al2sii)03 



(al3si2)05 



(alaSi.lOi 



(aLsi2)04fli 



(a'aS'^los 



(alasijlos 



(al3si3)06 



(al|iSi5)0ii + laq - (aq = 4 ■ 56) 



(zriSi,)02 



(zrisii)o.i-l-5aq - (aq = 4-70) 



(zrisii)o, 



{,n:»^)o-^ 



(fiiSiaK + èaq 



Ckys. 



Orthorh. 



Orthorh. 



Clinorh. 



Orthorh. 



Anisom. 



Clinorh. 



Clinorh. 



Clinorh. 



Tetrag. 



Tetrag. 



Tetrag. 



Tetrag. 



which, from the details given, would seem to be a hydroperspathoid, having the atomic 

 ratios for alumina and silica of the peradamantoid worthite. We may perhaps hope for the 

 discovery of further examples of this tribe and also of perspathoids. 



§ 06. The adamautoid persilicates constitute a characteristic and remarkable group. 

 Of the aluminic species, we find dumortierite, andalusite, fibrolite, bucholzite and 

 worthite, with differing atomic ratios, and in one case hydrous, all presenting the same 

 value for V ; besides the remarkable oxyflnorid, topaz, and the more highly condensed 

 kyanite and xenolite, the latter two having a smaller atomic volume than any other 

 silicates known. A single ferric species, anthosiderite, appears, and more than one 

 zirconic species. 



It is known that minerals, having the crystalline form and the centesimal composi- 

 tion of zircon, present variations in density from 4.86 to 4.02. The careful studies of A. H, 



Sec. III., 1S85. 10. 



