374 S. L. Penfield — Spang olite, a new copper mineral. 



were obtained from cleavage-planes. Inclined to the base the 

 crystals usually broke with a conchoidal fracture ; in only one 

 case a distinct cleavage was observed parallel to the pyramid 

 p, the angle of the cleavage measured on to the base being 

 63° 28', calculated 63° 33£'. Thin plates of the mineral are 

 non-elastic and brittle. 



Etching. — Experiments made by etching the mineral with 

 acids gave results which add very much to a proper understand- 

 ing of the crystals. It is readily soluble in dilute mineral 

 acids and the perfect basal cleavage makes it easy to obtain 

 orientated sections suitable for etching. The figures differed 

 both with the character and strength of the acid, but always 

 showed a decided hemihedral and rhombohedral symmetry. 

 Fig. 3 represents the character of some etchings produced by 

 dilute sulphuric acid. The figures which are very perfect are 

 about •066 mm in diameter and have the shape of a section across 

 a scalenohedron. Some of the depressions are bounded below 

 by a basal plane, others taper to a point while the scalenohe- 

 drons oscillate and give rise to delicate striations which are 

 beautifully brought out under the microscope by a slight change 

 of focus. The obtuse angle of the scalenohedron section meas- 

 ured under the microscope was about 133°, from which we 

 calculate that its relation to the lateral axis is a : \a : ^a, 

 which requires an angle of 133° 10'. Fig. 4 represents some 

 etchings produced by very dilute sulphuric acid : l cc of con- 

 centrated H 2 S0 4 diluted with 80 cc of water. These also have 

 a scalenohedral cross section and are about -06 mm in diameter. 



be 



The obtuse angle of the cross sections measures about 152 

 from which its relation on the lateral axes a:^a:4:a can 

 calculated, which requires an angle of 152° 12'. There are 

 also some steep rhombohedral depressions, with somewhat 

 curved contours developed on this section. Some of the etch- 

 ings produced by hydrochloric acid are shown in fig. 5, where 

 the hexagon is divided into three parts. The figures shown in 

 part a represent deep hexagonal depressions whose cross sec- 

 tion is that of a pyramid of the second order, these have a 

 diameter of about *035 mm and are surrounded above with shal- 



