470 H. B. PATTOX — THOMSONITE, MESOLITK, AND CHABAZITE 



For the purpose of checking analysis number 3 a corroborative test 

 for silica was made on another sample of mesolite, which gave SiO = 

 44.83. 



The following description of the method pursued in the analysis of 

 mesolite has been furnished by Doctor Hartmann. The mineral was 

 air-dried and analyzed by the method customarily employed with sili- 

 cates decomposed by HC1 . H 2 Q was determined by cautious ignition at 

 a low red heat, and the residual silicate used for further analysis. The 

 silica was treated with ammonium fluoride and Na,S0 4 to test the purity. 

 The sodium was weighed as sulphate obtained by ignition of the salts of 

 the evaporated filtrate from the calcium determination with H 2 S0 4 . 

 Platinum vessels were used wherever possible. 



Charazite 



Chabazite is the commonest of the zeolites found on the Table moun- 

 tains at Golden. It forms thin crusts lining the smaller cavities, and is 

 invariably the oldest mineral deposited. It is difficult, however, to secure 

 good specimens of this mineral without retaining a large piece of the 

 inclosing basalt. This is due to the brittleness of chabazite and to the 

 fact that the crusts are always very thin, so that when separating from 

 the rock the fragile crusts break into small fragments. 



In their description of this mineral as it occurs on North and South 

 Table mountains Cross and Hillebrand state that it occurs in simple 

 rhombohedrons or in plain rhombohedrons twinned parallel to the basal 

 plane. With the exception of the locality from which the zeolites de- 

 scribed in the present paper were obtained, it is true, as far as the obser- 

 vation of the writer goes, that the chabazite crystals are invariably simple 

 or twinned rhombohedrons. It is all the more surprising, therefore, to 

 find that at this particular quarry the chabazite crystals possess a far 

 more complicated form than has been observed before. 



The chabazites of this locality vary from white to reddish in color, 

 and in size from 5 to 10 millimeters. Not infrequently both white and 

 reddish crystals may be found on the same specimen. There are a few 

 simple rhombohedrons that show interpenetrating twinning such as 

 are to be seen at other localities on the same mountain; but in nearly 

 all cases the form is not only twinned, but is quite complex. The fol- 

 lowing forms may be identified on most of the crystals: -[--ft (1011), 

 — 2 R (0221) = s, — i R (0112) = e, oo P2 (1120) == a ; also two scaleno- 

 hedrons. 



Figure 2 of plate 49 is intended to represent one of these twinned 

 crystals in its customary development. In the general distribution of 



