76 



THOMAS STEERY HUNT ON A NATURAL SYSTEM IN 



Beginning with the most basic of the clays, we have given in Table XIV their atomic 

 formulas, with the values of P and V, so far as these can be determined. 



§ 100. The genesis of these persilicates, whether phylloid or colloid, here demands con- 

 sideration. The subaerial decay of the aluminous spathoids, orthoclase and albite, is 

 apparently the direct source of ordinary kaolin, for which the ratios of protoxyd, alumina, 

 silica and water are 0:3:4:2. The derivation of this from feldspars, having for the 

 same elements the ratios, 1 : 3 : 12 : 0, is due to the loss of all protox5'ds and two thirds of 

 the silica, and the hydration of the residue. The adamantoid and phylloid aluminous 

 protopersilicates are not generally subject to such transformations, although Damour has 

 described a silicate with the composition of kaolin, derived from the decay of beryl. 

 It is important in this connection to study farther the subaerial decay of other aluminous 

 spathoids, regarding the results of whose transformations very little is known. The 



XIV. 



Tribe 15. Argilloid. 



Species. 



FoRsiri.A. 



Sclirotterite. - - 

 Collyrite. - - - 

 Allophane. - - 

 Samoite. - - - 

 Halloysite. - - 

 Kaolin. - - - - 

 Keramite. - - - 

 Wolchonskoite. - 

 ]\Ioiitmorillonite. 

 Chloropal. - - - 

 Cimolite. - - - 

 Smectite. - - - 



(al4sij)05+5aq - 

 (al3sii)04 + 4iaq 

 (al3si;)Oj+6aq- 

 (al,sii)02 + 5aq - 

 (al3si4)Oj + 3aq - 

 (al.sii)o, + 2aq - 

 (al.,si3)05+2aq- 

 (crjsi3)0i + 3aq- 

 (aliSi^)03 + 2aq - 

 (fi,sij)03 + ljaq 

 (alisi3)04 + laq- 

 (aliSi4)o5 + 4aq- 



12-80 

 12-53 

 12-27 



13 -SO 



13-00 

 13-57 

 14-20 

 12-55 



D 



2-15 

 2-15 

 1-89 



2-40 



2-04 

 2-87 

 2-30 



5-95 



5-83 

 0-52 



G.ù7 

 5-42 

 617 



kaolin of Passait, in Bavaria, coming from the decay of a scapolite, of which it sometimes 

 retains the external forms, differs alike in its composition and the process of its generation 

 from the kaolin of orthoclase or albite. The scapolite of Passait is ekebergite, with the 

 atomic ratios, 4:9:18, or, if we compare its formula with that of albite, has for protoxyds, 

 alumina, silica and water, 1^ : 3 : 6 : 0. The resulting aluminous silicate gives, accord- 

 ing to the analysis of Von Ftichs, not 0:3:4:2, but 0:2:3:2 (= silica 46.4, alumina 

 35.0, water 18.6). This distinct and hitherto unnamed clay may be called " keramite," and 

 is remarkable as resulting from the decay of a spathoid near in composition to labradorite, 

 the ratios for which are 1:3:6:0. A similar kaolinizatiou of labradorite M^ottld 

 involve the removal with the protoxyds of only one fourth of the silica. The possible 

 results of such a transformation of this and related feldspars, great quantities of which 

 exist in the earlier crystalline rocks, are important alike in relation (o the soluble matters 

 removed and the residual aluminous silicates, both of which, in past ages, must have 

 played a considerable part in the chemistry of sea and land. 



The apparent kaolinizatiou of leucite, is remarkable in its chemical result. It was 

 shown by Rammelsberg that the crystals of white and kaolin-like leucite found at Rocoa 



