SOME CRYSTAL MEASUREMENTS OF CHILL AGITE. 209 



From this report it appears that three types of crystals 

 were present. 



(1) Transparent orange coloured plates. 



(2) Partly transparent orange coloured and partly 



translucent lemon yellow plates. 



(3) Translucent lemon yellow plates. 



The first were shown to be definitely wulfenite. In the 

 third the percentage of tungstic acid is fairly constant, 

 varying from 21.1 to 23.5 per cent. The lead oxide was 

 also constant where determined. The second group of 

 crystals were intermediate in both physical properties and 

 chemical composition to the first and third groups. 



The crystals supplied to us by Mr. Ullmann possessed 

 the physical characters of the third type being translucent 

 lemon yellow crystals. 



They were set in a gossan matrix commonly having two 

 edges embedded and the other two free. Where the crystals 

 were grouped, they either formed an irregular cell structure 

 or were arranged with an approximate parallelism of the 

 basal planes. In two of the crystals measured three edges 

 were present, but in the remaining five only two edges 

 could be obtained. As the crystals actually measured 

 were small, varying from 1.5 to 3 mm. in diameter, they 

 could not be analysed. 



They were flat thin square crystals, the edges being up 

 to 1 cm. in length and about 2 mm. in thickness. The basal 

 planes were large and the pyramid faces of the first order 

 well developed. These appeared to make but relatively 

 small angles (less than 30°) with basal planes. The crystals 

 were extremely brittle and fragile, and only fragments 

 could be obtained for measurement. 



The following tables give the measurements recorded for 

 the crystals. These were read on a two circle goniometer. 

 The explanation of the tables is as follows: — 



>"— Dec. i, 1012. 



