WOLFF AND MELCZER. — HARDYSTONITE AND SCHEFFERITE. 115 



b. Zinc Schefferite. 



While visiting the mine in September, 1898, my attention was called 

 by Mr. Van Mater, Superintendent at North Mine Hill, to a peculiar 

 pyroxene which was then coming out from the workings at the Parker 

 Shaft, and abundant material was then secured from the ore sorting belts 

 in the concentrating mill. The mineral occurs in large foliated masses, 

 associated with franklinite, willemite, and small grains and masses of a 

 white zinc mineral (to be described in the future), which often lies in 

 thin films parallel to the basal planes of the pyroxene. The latter has a 

 light-brownish red color in the large masses, while another variety occur- 

 ring in small grains in the zinc ore has a deep brown color. The most 

 striking physical feature is the (apparent) basal cleavage, which is as 

 perfect as that of feldspar, in addition to the ordinary prismatic pyroxene 

 cleavage. 



The angle between the two prismatic cleavages was determined by the 

 reflecting goniometer as 92° 59', between the basal cleavage and the prism 

 as 79° 02'. In a thin section parallel to (010) the angle (3 between the 

 basal cleavage and c' was determined as 74° 25'. It is readily seen in 

 this clinopinacoidal section that the apparent cleavage parallel to the 

 base is due to the development of gliding planes, for the basal cleavage 

 planes enclose thin lamellae which are evidently in the position of twins 

 parallel to the base with reference to the main mass of the mineral. 



The thin sections show the usual optical character of monoclinic py- 

 roxene, — one optic axis is approximately perpendicular to the base ; on 

 the clinapinacoid the axis of least elasticity c makes an angle of 40° 35° 

 with c', lying in the obtuse angle (3. 



The following analysis shows that the mineral is a zinc schefferite ; 

 it was found impossible to completely decompose the mineral with IIF, 

 hence FeO was not determined. 



