Ford and Bradley — Hetcerolite from Leadville. .601 



W. T. Schaller, of material from the original locality. This 

 analysis was considered to confirm Moore's formula, and to 

 establish the mineral as a distinct species. The mineral was 

 stated, in this article, to be tetragonal, as shown by the optical 

 behavior of the fibers under the microscope, and to have an 

 indistinct prismatic cleavage. Specific gravity was given as 

 4*S5. The analysis by Schaller is quoted in a later paragraph. 



The hetaerolite from Leadville was found on the "W of tone 

 property, at a depth of about TOO feet below the surface. It 

 occurs as an occasional vug-filling mineral at the lower contact 

 of the blue limestone with a quartzite. It is associated with 

 calamine crystals and with smithonite. It has a radiating, 

 mammillary structure. In general, the outer surfaces are 

 smooth and rounded, but in one cavity of the specimen they 

 are covered with a drusy coating of microscopic crystals. 

 These are much too small, however, to admit of any measure- 

 ments being made. When broken the radiating masses show 

 a prismatic structure similar to that observed on many speci- 

 mens of gcethite and manganite. Under the microscope, the 

 very fine fragments become transparent, having a dark brown 

 color. They show birefringence and have an extinction par- 

 allel to the prismatic edges. JSio further evidence of its crystal 

 system could be discovered. The index of refraction was 

 determined to be greater than 1*78, by noting the effect upon 

 the small fragments when immersed in a liquid having this 

 index of refraction. 



The mineral shows a splintery fracture. Its hardness is 

 between 5*5 and 6. The specific gravity was determined as 

 4'6. Its luster is submetallic. Its color is dark brownish to 

 black, with often a bright varnish-like exterior. It gives a 

 dark chocolate-brown streak. 



It is infusible. On charcoal with sodium carbonate it gives 

 the characteristic zinc oxide coating. With the fluxes it gives 

 the color reactions indicative of manganese. It is easily sol- 

 uble in hydrochloric acid, giving off chlorine gas. It yields 

 water when heated in the closed tube, but does not give off 

 oxygen gas. 



The method of analysis was briefly as follows : The water 

 was determined by the direct method of Penfield." The resi- 

 due from this determination was dissolved in hydrochloric acid 

 and silica determined as usual. The filtrate from the insoluble 

 silica was evaporated to dryness in order to remove the hydro- 

 chloric acid. The residue was dissolved in about 200 cc of 

 water. To this 50 cc of formic acid was added and an aqueous 

 solution of about 3 grams of sodium acetate. This solution 

 was warmed to about 60° C. and the zinc precipitated by 

 *Tkis Journal, xlviii, 31, 1894. 



