SCHaller.] DUMORTTERITE. 93 
color is blue, sometimes nearly black. Inclusions are not prominent, 
though bubble's and rutile have been noticed. 
The axial piano is parallel to 5{010}. Bx a (negative) perpendicular 
to c {00l}. In the twins the axial planes of the two parts make an 
angle of about 60 . /?isabout L. 65, and the birefringence is about .010. 
The axial angle (2 V Na ) is near 35 to 4<» . The dispersion is ener- 
getic p<v. Pleochroism is very strong; h = c, colorless or very pale 
blue; a, cobalt blue or violet. Some of the specimens from Brignais 
are of a rose-salmon color, a little redder than andalusite. The maxi- 
mum absorption is (contrary to that of tourmaline) in the direction of 
elongation (parallel to 6). The presence of idiophanous figures is also 
noted. According to Damour, the blue color of the mineral may per- 
haps be due to traces of Ti 2 3 , the presence of which in the French 
mineral has, however, not been demonstrated. It is noticed that the 
small fibers of dumortierite are often inclosed in a white mica, which 
is gradually replacing the original mineral. 
GERMANY AND AUSTRIA. 
The mineral is found near Schmiedeberg, Silesia/' in the pegmatite 
of the lower Val Donbastone, in long libers of a green or greenish- 
blue color. These fibers have a thickness of 1 mm. and reach a maxi- 
mum length of 50 mm. They are often bent, and inclose pieces of 
quartz. On one liber a prism angle of 69° 6' was measured. Pris- 
matic cleavage, imperfect, was noted. The pleochroism is very strong: 
!c=b, colorless; a, pistachio-green. Cross sections show the emer- 
gence of an acute bisectrix (negative), the axial angle being somewhat 
smaller than that of muscovite. With a crystal refractometer the 
following values for the indices of refraction were obtained: 
or=1.678 
/?= 1.686 
r=1.689 
y—a— .011 
An analysis of impure material was also made. 
In a clayey residue, the mineral has been found at Imligan, near 
yhodan, and Schobrowitz, near Carlsbad, in Bohemia, and in clayey 
andstone at Oberbris, near Pilsen, in Bohemia. These residues are 
)robably formed from decomposing pegmatite, from which the dumor- 
ierite originally came. The mineral shows a strong pleochroism; 
, deep carmine to smalt blue and, in places where partly decom- 
osed, dark olive to red brown; ft, light gray olive to colorless. The 
egative) acute bisectrix is parallel to the elongation. The obtuse 
II jisectrix is perpendicular to the cleavage plates (#={100}). The 
aSee Literature, pp. 119-120. 
