144 PHYSIOGRAPHY. 



Quartz. 



49'. P on m =152 51'. (pentahexaedre. HAUY.) Rare. 

 Fig. 372. r on a? =167 56'. z on x =125 II 7 . P 

 on o?=148 42'. (plagiedre. HAUY.) Rare. Fig. 373. 

 Similar to Fig. 372, with the addition of the rhomboidal 

 truncations of Fig. 367, and the replacement of the edges 

 between s and x; s and x =152 13'. u on x = l7o 33', 

 (co-ordonnee. HAUY.) Very rare. Fig. 374. P on o = 

 160 15'. o on o = 125 10'. Very rare. 



Irregular forms and grains. 



Cleavage, parallel to P and r; but very imperfect, and 

 interrupted by conchoidal fracture. Fracture conchoidal, 

 sometimes highly perfect, sometimes less distinct. Sur- 

 face, a and x generally rough ; r and z are streaked hori- 

 zontally. The rest of the faces generally smooth. 



Lustre vitreous, inclining in some varieties to resinous. 

 Color, white, prevalent ; among the brightest colors are 

 violet-blue, rose-red, clove-brown and apple-green. Dark 

 brown and green colors, generally owing to foreign admix- 

 tures. Streak white. Transparent . . . translucent, fre- 

 quently even opake, particularly when impure. 



Hardness =7-0. Sp. gr. =2-690. 



Compound Varieties.' 1. Faces of composition paral- 

 lel, axis of revolution perpendicular to a face of. r; the in- 

 dividuals being continued beyond the face of composition. 

 2. Individuals joined perpendicular to the axis. Frequently 

 large crystals are made up of alternating laminae .of two in- 

 dividuals ; and often, faces of composition assume the ap- 

 pearance of cleavage. 



Implanted globules, reniform, stalactitic shapes : surface 

 smooth, granulated, or drusy ; composition columnar, gen- 

 erally impalpable ; often a second time composed into gran- 



