Jamesonite Group, from Two Localities. 69 



The Gold Hunter specimens occur in quartz and consist 

 of fine matted, wool-like masses of dark gray fibers and 

 compact, steel-gray fibrous material having somewhat 

 the appearance of Astrakhan fur. The fine fibers in the 

 cavities rest upon a base of small quartz crystals or of 

 translucent buff crystals of siderite. The matted aggre- 

 gates also contain scattered, minute, perfect crystals of 

 quartz and siderite. 



Crystallography. — The crystals of mullanite are pris- 

 matic needles, deeply striated and somewhat flattened 

 parallel to the brachypinacoid. On the specimen from 

 the Iron Mountain Mine, the free needles are truncated 

 by a terminal face which is perpendicular to the pris- 

 matic direction and was taken as the basal pinacoid. 

 The crystals are provisionally considered orthorhombic. 

 The prism zones of the crystals from Iron Mountain do 

 not yield reflections of the signal and only after trying 

 a dozen or more, was a very minute needle found which 

 gave reflections indicating the forms shown in fig. 1. All 

 attempts to refer the observed faces to the axes of diaph- 

 orite and freieslebenite were unsuccessful. The prism 

 m in the drawing was taken as the unit prism (110). 

 Only a single crystal was found in the material from the 

 Gold Hunter Mine, which gave even approximate values 

 for the interfacial angles. This was a deeply striated 

 prism, flattened parallel to (010), broken at both ends 

 and having essentially the form shown in fig. 2. The 

 value for the a-axis on the crystal shown in fig. 1 was 

 0.85, and on the crystal fig. 2 was 0.82. Provisionally the 

 mean between these is taken to represent the length of 

 the a-axis in terms of the &-axis, thus : 



a : b : c = 1 : 0.835 : x 



The forms observed on the two crystals measured are 

 then : 



a(100) ro(110) »(130) 



6(010) r(120) *(140) 



c(001) j8(510) 



It should be remembered, however, that the measure- 

 ments were based upon barely perceptible reflections of 

 the signal, or in some cases, upon light reflected from the 

 faces. The crystallographic data are certainly subject 

 to revision should well-crystallized material be found. 

 Some very minute fibers from a cavity in quartz in one 

 of the Gold Hunter specimens, examined under the 



