x Proceedings. [October i6th, 1906. 



The latter quantity, W, is termed the " valency volume," and 

 the equivalence parameters are : — 



.,/ aW~ , 



X = " — : : — — : , y = x a. z — cv. 



v ^sin a sin /j sin 7 



As an indication of the value of the method of calculation 

 here indicated may be shown the simple interpretation which it 

 affords of the long known, but hitherto unexplained, crystallo- 

 graphic relations existing between the so-called humite minerals, 

 namely : — 



Chondrocyte, Mg 3 (Si0 4 ). 2 , 2Mg(F)(OH)...Monosymmetric. 



Humite, Mg B (Si0 4 ) 3 , 2Mg(F)(OH) Orthorhombic. 



Clinohumite, Mg 7 (Si0 4 ) 4 , 2Mg(F)(OH) ..Monosymmetric. 



Prolectite, MgSi0 4 , 2Mg(F)(0H) Monosymmetric. 



Forsterite, Mg 2 Si0 4 Orthorhombic. 



The crystallographic data for, and the equivalence para- 

 meters of, these minerals are given in the following table : — 





W 



a : b : c 



x : y : z 



z\W 



Chondrodite 



38 



1 '08630 : 1 : 3*14472 



2-4249:2-2323: 7-0199 



0-18473 



Humite 



54 



i - o8o2i : 1 : 4*40334 



2-4278:2-2475: 9-8965 



0-18327 



Clinohumite 



70 



1-08028 : 1 : 5-65883 



2-4349: 2-2540:12-7547 



0-18221 



Prolectite... 



22 









Observed.. 





i - o8o3 : 1 : i"8862 



2-3877:2-2102: 4-1689 





Calculated 





1 '082 2 : 1 : 1 "8500 



24292:2-2446: 4*1526 





Forsterite ... 



16 









Observed.. 





C9296 : 1 : I , i7i4 



2-4492:2-2769: 2*8691 





Calculated 





0^9240 : 1 : i , i8o4 



2-4292:2-2446: 2-8674 





