ART. 19. 



MORDENITE — ROSS AND SHANNON. 



If) 



and incloses mordenite and spherulitic quartz. No other mineral is 

 deposited on the analcite, and it is probably the youngest of the 

 minerals represented in the Challis specimens. 



CHLORITE. 



About one-fourth of the total number of small pebblelike fillings 

 in the amygdaloid rock consist of a soft, foliated, brownish-green 

 chlorite. These chlorite fillings, which reach an extreme diameter of 

 7 millimeters, are easily freed from the surrounding matrix and when 

 crushed yield a homogeneous sample for analysis. This chlorite does 

 not occur in the same vesicles with any of the zeolitic minerals, but 

 it is sparingly distributed in the silicified portions of the inclosing 

 rock near the large zeolite-filled cavities. Under the microscope the 

 chlorite is seen to consist of yellow-green irregular folia. These are 

 biaxial and optically negative ( — ) with 2V near 15°. The indices of 

 refraction, which are high for a chlorite are, «= 1.615, i8= 1.637, 

 7=1.638, 7 — a! = 0.023. The mineral is strongly pleochroic with X 

 and Y olive-green and Z brownish-yellow. This material was 

 analyzed yielding the following results and ratios: 



Analyses and ratios of brownish-green chlorite. 



Constituent. 



Per cent. 



Ratios. 



Si02-.. 



AI2O3 



FezOs 



FeO 



MnO 



CaO 



MgO 



H2O+110°C 

 H2O-110°C 



Total. 



30.76 

 12.12 



9.12 

 22.76 



1.24 



Trace. 



12.36 



9.76 



1.80 



99.92 



.307j 

 .542\ 

 .100/ 



0. 



170 X 3 

 .176 X 1 



.160 X 4 



.160 X 4 



1 00 X 3 

 1.03 X 1 



.94 X 4 



.94 X 4 



This analysis yields as the formula, 4RO.R2O3.3SiO2.4H2O, with 



R0 = M20 : FeO = l : 1 and 



R203 = Fe203 



AL0,= 1 : 2. This can 



not be definitely assigned to any member of the chlorite group but is 

 most closely related to diabantite and delessite, chlorites occurring 

 characteristically as amygdule fillings in basic igneous rocks. The 

 content of ferric iron is noteworthy, and this doubtless explains the 

 relatively high index of refraction and birefringence of the mineral. 

 In a recent description of diabantite from Nova Scotia, Walker ^ ob- 

 tained from an analysis a formula slightly different from that of 



Thomas L. Walker. Univ. Toronto Geol. Series No. 14, p. 47, 1922. 



