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University of California Publications in Geology [Vol. 10 



have not been entirely leached out, in the hydration and silication of 

 the latter mineral, and therefore have no part in the formula for crest- 

 moreite. An hydrous lime silicate is forming by the alteration of the 

 wilkeite and the ratio of CaO : Si0 2 will be as 1 : 1 no matter how much 

 water, or in what way, it enters into the composition. 



Crestmoreite can be represented by the simple formula CaSiO,-H 2 

 which requires 



Si0 2 44.78% 

 CaO 41.79 

 H 2 13.43 



This would make it a simple hydrous metasilicate like a hydrous wol- 

 lastonite, but it seems more probable that crestmoreite, from the water 

 determinations and derivation from wilkeite, is a hydrous basic ortho- 

 silicate. 



The following percentages of water were given off at the respective 

 temperatures : 



At 102° 1.25% 

 200 3.27 

 300 10.27 

 Bed heat 15.11 

 Blast 16.76 



In view of the fact that most of the water is expelled only at the 

 higher temperatures it can be regarded as constitutional, and the above 

 formula can be written H 2 CaSi0 4 . 



Wilkeite is represented by the formula 3Ca 3 (P0 4 ) 2 • 3Ca 2 Si0 4 • 

 3CaS0 4 • CaC0 3 • CaO, and it can readily be seen how the orthosilicate 

 can increase at the expense of the more soluble phosphate and sulphate 

 through the wilkeite alteration by carbonated and silicated waters. 

 These waters were the heated ascending solutions which brought about 

 some of the later crystallizations, and in the formation of the ortho- 

 silicate part of the calcium was replaced by basic hydrogen. The 

 exact formula for crestmoreite depends upon the water and therefore 

 no formula can be advanced that is not open to criticism. As a basic 

 silicate most of the water must be considered as constitutional. 



The formula proposed for crestmoreite is 4H 2 CaSi0 4 -|-2H 2 0. 

 This requires : 



Si0 2 43.32% 



CaO 40.43 

 Constitutional ILO 12.99 } 

 Crystallization H 2 3.26 ^ 16-2 ° 



100.00 



