302 Hillebrand and Washington — Minerals from Utah. 



supposition that the CaC0 3 found by him and later by Frenzel* 

 and Church (1. c.) is not an essential constituent of tyrolite. 



It is improbable that more than a very small quantity, if any, 

 chalcophyllite was mixed with the material analyzed under I 

 and II, although both appeared on some of the specimens marked 

 tyrolite received from Mr. Pearce, and are not always easy 

 to distinguish. In any mixture of tyrolite and chalcophyllite 

 the water found must exceed its percentage in the former min- 

 eral. This is here not the case, whence it is to be inferred 

 either that the present mineral is not tyrolite or that the older 

 analyses do not represent its true composition. 



A large portion of the water is very loosely combined. Of 

 that in analvsis I, 4*69 per cent escaped at 100° C, the most of 

 it over sulphuric acid ; and in analysis II, 4*15 per cent was re- 

 moved by sulphuric acid, and further - 91 per Cent escaped at 

 100° C, making a total of 5*06 per cent. These amounts sub- 

 tracted from the total percentage found leave 12 - 57 and 12*51 

 per cent respectively, or about five molecules (assuming five 

 molecules, (CuO(CaO)). At 280° C. the loss on sample II was 

 10 "34: per cent, in which is presumably included the water of the 

 gypsum supposed to be present, leaving three molecules firmly 

 combined. Church (1. c) likewise noticed a great loss of water 

 in vacuo and at 100° C, but assumed that it was hygroscopic 

 water included between the plates of the mineral. The second 

 of his analyses with data for calculating the percentage compo- 

 sition is as follows : 



Substance 0-4585 CuO 5006 



H 2 in vacuo 0024 As 2 5 29-29 



H 2 at 100° 0-011 H 2 [8-73] 



CaC0 3 0-0505 0aC0 3 11*92 



CuO 0-2 L2 



Mg 2 P 2 7 0-205 1 00-00 



whence he deduces the formula 5CuO, As 2 5 , 4R 2 0. Assum- 

 ing that Mg 2 P 2 7 is an error for Mg 2 As 2 7 , or for As 2 S 3 , in 

 which latter form it appears that arsenic was usually estimated 

 by him in minerals of a similar character, it is impossible to 

 deduce the above given percentage for AsX) 6 . But considering 

 the latter correct, and including the water lost in vacuo and at 

 100°, the composition is : 



CuO ■ 46-24 



Aso0 5 27-05 



H 2 6 15-70 



CaC0 3 •_ , 11-01 



100-00 



which furnishes the molecular ratio CuO : As 2 5 : H 2 as> 

 5*00 : 1"01 : 7'43, not greatly differing from those derived from 

 analyses I and II above. 



* Naumann-Zirkel, Elemente der Mineralogie, p. 540. 



