Geology and Mineralogy. 229 
t 
aris, July 1st, 1876, gives the results of his researches in regard 
to the optical characters of chondrodite. These results are of 
especial interest as proving for the Swedish chondrodite, and the 
esuvian humite what has been shown by the writer to be true 
of the chondrodite from Brewster, N. Y.,—that the second and 
third types are monoclinic, not orthorhombic. 
The principle conclusions of M. DesCloizeaux are, as follows. 
The three types of humite, described by Scacchi, constitute three 
different species, closely related to each other in regard to form. 
The erystallographical and optical characters of the types are the 
following: Type I, humite from Vesuvius. Orthorhombic. . 
damental angles, as measured, * 4 ,¢°( pet=001 A 201)=108° 47’, 
Aji? (pat=001 ,013)=124° 16’. The plane r® is made the fun- 
damental pyramid with A Ar® (pb?=001 A 111)=101° 39’, and 0? 
is made the unit prism, B~o?(100110)=114° 50’. Plane of 
the optic axes parallel to the base, with the acute bisectrix paral- 
lel to the shorter diagonal of the base. Dispersion weak, perhaps 
v; 2Ha (red rays) =78° 18’ — 79°. 
Type II, chondrodite from Sweden. Monoclinic. Fundamental 
bands aries with every specimen examined. Apparent axial 
nee (in oil), red rays, 86° 27’, blue, 86° 38’. Bisectrix positive, 
Dispe 
nante). In several other crystals the axial angle was found to 
0’ 
AU (pe'=001 4 011=125° 13’); Cars (gim=010 A 110)= 154) 
(pd$=001 .111)= 195° 47’, A n75=001 a 111)=119° 17’. Plane 
ptic axes inclined to the front edge and making an angle 
of about 11° with the base. Dispersion of the axes feeble par. 
— also crossed, scarcely appreciable. Bisectrix positive 
84° a ane of symmetry. Axial angle (in 
oil), red rays, 
in appearance 
a letters given are those of Scacchi, the symbols which follow are those of 
!zeaux, in his own and in Miller’s method of notation. 
A*. Jour. Sct.—Turmp Serres, Vou. XI, No. 69—S#Pt., 1876. 
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