438 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



crystals on each specimen of this material; often two distinctly dif- 

 ferent types of crystals occur on opposite sides of the same specimen. 

 The United States National Museum collections contain three large 

 exhibition specimens of this Utah material which have not, hereto- 

 fore, been examined crystallographically. A study of these crystals 

 shows them all to be somewhat different in development from the 

 Utah anglesites already described. A single form new to the species 

 was observed, together with two additional forms not previously 

 found on the anglesite from this locality. 



The anglesite from the Tintic district or from Eureka, as it is 

 generally labeled, occurs as brilliant adamantine crystals like those 

 of Monte Poni implanted in cavities in solid masses of granular 



galena. They are usually highly lus- 

 trous and perfectly transparent and 

 limpid. The smoky tint so common 

 in the Sardinian specimens is rarely 

 encountered, and the dull, pitted, and 

 opaque appearance so characteristic 

 of the Pennsylvania crystals is en- 

 tirely absent in the Utah, as in the 

 Idaho anglesites. 



The specimens of galena on which 

 these crystals occur are too large to 

 be displayed in the systematic min- 

 eral collection, and are now in the 

 exhibition series of lead-silver ores. 

 The first of these (Cat. No. 63717) 

 is from the Eureka Hill mine, Tintic 

 district, and was jDurchased from 

 George L. English & Company in 

 1895. It consists of a large mass, 

 weighing approximately 5 kilograms, 

 of granular galena, containing par- 

 allel streaks and inclusions of gray limestone. About one-third of 

 the broad surface of this mass is occupied by a flat cavity completely 

 lined with brilliant transparent colorless crystals of anglesite, which 

 reach a length of 1 centimeter. Scattered among the anglesite crys- 

 tals and at times included in them are small globules of greenish 

 translucent native sulphur. The crystals on this specimen are all of 

 the same habit. They are prismatic parallel to the vertical axis, the 

 dominant forms being the unit prism m(llO) and the pyramid 

 ^(324). The forms observed on this type of crystal are a(lOO), 

 m(llO), c(OOl), ^(102), o(Oll), «/>(012), s (111), 2/(122), and ^(324). 

 The faces are clear and yield sharp signals. The prism zone is 

 commonly striated parallel to the c axis by oscillation between the 

 front pinacoid a(lOO) and the prism m(llO). The forms and ap- 

 pearance of these crystals are shown in figure 2. 



Fig. 2.— Crystal of anglesite. 



