Clarke and Steiger — Action of Ammonium Chloride. 33 



seemed to be desirable to determine whether a more prolonged 

 treatment would produce any greater effect. Accordingly a 

 third lot of thomsonite was mixed with ammonium chloride, 

 and heated in a sealed tube to 350° for 24 hours. The leached 

 product contained 3'40 per cent of ammonia, a distinct increase 

 over the other findings ; although the amount of transforma- 

 tion into an ammonium salt was still only moderate. 



We have already seen that stilbite, heulandite and chabazite 

 approximate more or less nearly to trisilicates in their composi- 

 tion. Thomsonite, however, is essentially an orthosilicate, 

 with variable admixtures of trisilicate molecules. In the exam- 

 ple under consideration, ignoring water and soluble silica, the 

 molecular ratios give this formula : 



Na 112 C a , D1 AUSi s O s USiO,), M ; 

 or, condensing, 



R",.,A1, 80 X S78) = 1:2:2. 



Here the acid radicles are ten-elevenths orthosilicate. Ammo- 

 nium derivative " A," similarly computed, gives first — 



(NH,) JM Na 81 Ca 1 , 9 Al M8 (Si 3 O e ) 41 (SiOJ 5 „; 



or, uniting univalent bases with line, 



R" 292 A1 598 X 695 , = 1:2:2; 



the fundamental ratios being practically unchanged. 



It will be observed that in all of these computations of 

 formulae we have assumed that ail the water is " zeolitic " ; 

 that is, independent of the true chemical molecules. This 

 question, however, needs to be separately investigated for each 

 individual species. While the assumption is valid for some of 

 these minerals, it is not necessarily valid for all. The real 

 chemical differences between the zeolites are yet to be deter- 

 mined ; our work merely proves- that ammonium compounds 

 are formed, completely in some cases, partially in others. The 

 research should be extended to cover all the zeolites ; but this 

 task we must leave to other investigators. Silicates belonging 

 to quite different groups must now claim our attention. 



Ilvaite. 



This rare mineral was found by Mr. Waldemar Lindgren at 



the Golconda Mine, South Mountain, Owyhee County, Idaho. 



It occurs in jet black masses and occasional rough crystals, 



imbedded in quartz or calcite, and intimately associated with 



two other minerals which appear to be garnet and tremolite. 



Traces of pyrite also appear. The specific gravity of the 



ilvaite, as determined by Dr. Hillebrand, is 4*059 at 31°. 



Am. Jour. Sci. — Fourth Series, Vol. XIII, No. 73.— January, 1902. 

 3 



