Q. J. Brush— Oahniie from Mine Hill, N. J. 29 



Tlie crystals vary in diameter from an eighth of an inch to 

 over an inch and a half; generally, however, they are less than 

 half an inch. The color of the crystals is blackish-green; in 

 thin fragments, olive-green. Hardness =-- 7-5. Specific gravity 

 =4-89-4-91. 



Before the blowpipe the mineral is infusible. With the fluxes 

 reacts for iron and manganese ; and with soda on charcoal gives 

 a zinc coating. 



The analysis in the wet way was made by Mr. Joseph S. 

 Adam of this laboratory. The mineral was decomposed by 

 fusion with bisulphate of potash. Tlie silica was separated m 

 the usual manner, and the iron and alumina thrown down as 

 basic acetates, and this precipitate 

 purity. The iron was determined "" 



nate of potash. From the acetic soiuxion lue uiuugiuiccc » cv^ 

 separated by bromine, and the zinc was thrown down from the 

 filtrate by sulphid of ammonium. The smaU r * -^ —" 



nesia was determined as pyrophosphate, ^^ 



taken to separate the 



Alumina, . 



Zincoxyd, 39-39 



Manganous oxyd, . . - 1 "20 



100-11 



This gives the relation of the oxygen of it and fi as 8 12 : 25-77, 

 or 1:3-17, which would indicate that a small portion of the 

 iron was present as protoxyd. We have but to assume l-o6 

 per cent of the Pe in the analysis to have existed as Fe m the 

 mineral to reduce the ratio to exactly 1:3. 



This variety of gahnite shows a larger percentage ot zmc 

 than any heretofore analyzed, and is unique m its cubic habit. 

 It is associated with black mica, apatite, calcite and a brownish 

 variety of chrysolite. A partial analysis of this chrysolite by 

 W. G.Mixter shows it to be a unisilicate of iron manganese 

 magnesia and zinc, probably related to, and possible id^tical 

 with, the zinciferous chrysolite described by Prof. W. T 

 Roepper, in this Journal, II, 1, 35. A tin-white metallic mineral 

 imbedded in some of the gahnite crystals proved to have the 

 pyrognostic characters of leucopyrite. 



Sheffield Laboratory of Tale College, Nov. 1870. 



