196 F. W. Clarke— TschermaU s Theory of the 



nevertheless quite close to theory. It will 'be seen that the 

 value of K/ 2 in the second term of each expression is constant ; 

 that is, that we have either A1H 2 2 or the corresponding- ferric 

 radicle ; but the values of the first term are somewhat different. 

 In metachlorite, as in daphnite and chamosite, R/ 4 = A 2 MH; 

 in cronstedtite it is A 4 , and in delessite it is H 4 . In klementite 

 we have R / 4 = A 3 M; in diabantite, 3K/ 4 = M 4 H 8 ; and in eura- 

 lite 7R/ 4 =A 22 H 6 . Such ratios, however, are difficult to fix 

 sharply, because of the uncertainties in the water determina- 

 tions. In Heddle's analyses, however, the water given off at 

 100° is distinguished from that retained at higher tempera- 

 tures, and the results are correspondingly favorable to theory. 

 In his delessite, for instance, the water becomes partly water of 

 crystallization ; and the mineral from Bowling Quarry agrees 

 well with the formula 2Mg 3 (Si0 4 ) 2 A 4 , 2aq-f-Mg 2 (Si6 4 ) 2 H 4 ; 

 with about f of the magnesium replaced by ferrous iron. 

 Calculating the composition of each mineral from the formulae 

 given below, and comparing the results with the reduced 

 analyses from which the expressions were derived, we can 

 judge of the closeness with which the facts and the theory 

 agree. 



Metachlorite, 



Euralite, 



Diabantite, 



Klementite, 



Delessite, 



Cronstedtite, 



Aphrosiderite, 



4Fe„(SiO; 



7Mg"„(Si0 4 

 4Mg-;(Si0 4 



Mg,(sio 4 ; 

 M g ,(Sio 4 : 



Fe 2 (t3i0 4 )^ 



! 2 A 2 (FeOH] 



),R' 4 



>A M 



iH + Fe 3 (Si0 4 ) 2 A 2 

 + 3Mg 3 (Si0 4 ) 2 A 2 

 + 3Fe 2 (Si0 4 ) 2 A 2 



+Mg,(SiOJA 

 + 2Mg s (Si0 4 )„A o , 



t +4Fe 1 (SiOJ,(Fe' 

 Fe 3 (Si0 4 ) 2 A 2 



2aq. 

 "H 2 2 ) 2 





Metachlorite. 

 Found. Calc. 





Euralite. 

 Found. Calc. 



Diabantite. 

 Found. Calc. 



SiO„ 



23-82 



24-57 





37*74 



38-15 



34-05 



34-34 



A1„0 3 

 Fel0 3 

 FeO 



20-42 



20-88 





18-48 



19-45 



12-80 



12-51 



45'76 



44-23 









26-32 



26-49 



MgO 













30-91 



29-24 



16-70 



16-35 



H 2 



io-oo 



10-32 





12-87 



13-16 



10-13 



10-31 





100-00 



100-00 



100-00 



100-00 



100-00 



100-00 





Klementite. 

 Found. Calc. 





Cronstedtite. 

 Found. Calc. 



Aphrosiderite. 

 Found.' Calc. 



SiG 2 



28-85 



28-78 





21-18 



21-56 



24-54 



25-31 



Al.o, 



30-36 



30-57 











y.2-59 



21-52 



Fe 2 3 













35-74 



34-48 











FeO 











35-19 



36-20 



43-87 



45-57 



MgO 



28'73 



28-78 



















H 2 



12-06 



11-87 





7-89 



7-76 



9-00 



7-60 



100-00 100-00 



100-00 100-00 



100-00 100-00 



