﻿118 Cross and Eakins — Ptilolite, a new Mineral. 



Si0 2 _ 59"26 



Al 2 O s 23-63 



Fe,0 3 ___ ... -30 



FeO ___ .... -57 



CaO _ - _ 5-93 



MgO __ -31 



K 2 4-78 



Na 2 4-94 



HO -74 



100*46 



Analyst, L. G. Eakins. 



The various porous or amygdaloidal fragments found evi- 

 dently represent material from different positions in the orig- 

 inal rock-mass, and according to the former position of each 

 specimen there is a certain development of minerals in the 

 vesicles or pores. A reddish-gray, finely cellular rock contains 

 in some cavities creamy, banded opal, upon which a decided 

 play of reddish color was noticed in certain spots. Chalcedony 

 and quartz fill many cavities completely. Another rock speci- 

 men, in which the pores are all round and small, exhibits no 

 minerals in its cavities. A third specimen is very porous, the 

 pores being irregular though never greatly distorted. More 

 than half of these cavities contain a banded deposit of opal 

 and chalcedony, the banding having in all a parallel direction. 

 A few pores are filled by clear chalcedony. All cavities not 

 entirely filled in this manner show a crust of small, clear heu- 

 landite crystals of tabular form, with minute white globulitic 

 masses of unknown character scattered over and between them. 

 A still more porous rock in which the cavities are irregular 

 shows traces only of the creamy opaline deposit, while heu- 

 landite and white globules of the unknown substance form a 

 distinct crust. As a still more recent formation there appear in 

 the pores of this rock small tufts of a white mineral. These 

 are very delicate and could not be procured in sufficient quan- 

 tity for chemical examination. The resemblance to mesolite, 

 as it occurs in the basalt of Table Mountain, was so marked 

 that for a time the identity of the two substances seemed pos- 

 sible, but these tufts belong to the new mineral, found more 

 abundantly in other specimens. 



On the north slope of Green Mountain there are fragments of 

 this augite-andesite in some of which the white mineral in tufts 

 is specially well developed. The rock is light reddish-gray and 

 very vesicular, the pores being drawn out cylindrically in a cer- 

 tain direction. Many of these pores have been completely 

 filled by a solid mass of chalcedony and quartz, the latter occu- 

 pying the center. In other cavities there is merely a thin coat- 



