ORDER II. PRISMATIC HAL-BABY TE. 123 



tain combinations are rough, in others are per- 

 fectly smooth, while the reverse takes place in 

 other faces ; so that they do not constantly pre- 

 sent the same appearances. 



Lustre vitreous, inclining to resinous. Colour white, 

 prevalent ; inclining to grey, yellow, blue, red, 

 or brown. Among some more remarkable tints, 

 we notice smalt-blue, pale sky-blue, and almost 

 indigo-blue ; likewise wood-brown and hair- 

 brown. Bright red and yellow colours owing to 

 admixtures of hemi-prismatic and prismatoidal 

 Sulphur. Streak white. Transparent ... trans- 

 lucent. 



Brittle. Hardness = 3-0 ... 3-5. Sp. Gr. = 4446, 

 a white crystallised variety from Freiberg, the 

 same from the measurement of which the above 

 dimensions of the crystalline forms have been 

 derived. 



Compound Varieties. Globules, both imbedded 

 and implanted, also reniform shapes : surface drusy, 

 uneven and rough, composition either lamellar, 

 generally imperfect, or columnar, the latter often 

 very thin. In the reniform shapes the curved la- 

 mellar particles of composition consist of imperfect- 

 ly straight lamellar, or of columnar ones. Massive : 

 composition as in the imitative shapes, more fre- 

 quently distinctly straight lamellar masses are ag- 

 gregated in a granular composition. The compo- 

 sition is sometimes granular, and even impalpable. 

 Without coherence of the particles, friable. 



