DE. A. W. HOFMANN ON THE PHOSPHOETJS-BASES. 
481 
“ System monoclinic : — 
Forms observed: — 
10 0, 0 01 = 82° 36'. 
10 0, 010, 001 (Fig. 45). 
Fig. 45. 
10 0 , 010 
1 0 0 , 0 01 
010 , 0 01 
According to Naumann : — 
Fig. 46. 
Calculated. Observed. 
o < o / 
= 90 0 90 3 
= 82 36 82 36 
= 90 0 89 67 
y=82° 36'. 
Forms observed : — 
oo P oo, oo P oo, OP. 
According to Weiss : — 
coc=97° 24'. 
Forms observed : — 
fl!:oo 5 :ooc; ooq5:5:ooc; co a : oo b : c. 
According to Levy : — 
/i'P=97° 24'. 
Forms observed : — 
Combinations observed : — 
10 0, 010, 001 (Fig. 46). 
Cleavages 10 0, 010, 001 distinct and easily obtained, more especially 010. 
The crystals are elongated in the direction of the axis of symmetry, and often hol- 
lowed out for a great part of their length when rather thick, that is to say, when their 
sides attain the width of half a millimetre. The hollow has the form of a pyramid 
having its base on the face 010 and its apex towards the centre of the crystal The face 
010 is often reduced to a very narrow rectangular rim. The opposite apex of the 
crystal is irregular, as if it had adhered to the side of the vessel. The face 0 0 1 is in 
general rather more developed than 10 0. 
The crystals are optically negative. The plane of the optical axes is parallel to the 
line of symmetry [010]; the principal medium-line is perpendicular to the latter, and 
UDCCCLX. 3 s 
