Iron to the Optical Properties of Lithiophilite, etc. 389 
with white light, was similar to that of brookite, where the 
extreme colors of the spectrum, red and blue, are dispersed in 
planes at right angles to one another. 
Plane of the 
Indices of refraction|9Ha over axis optic axes, 
‘Loeality, color, and optical orienta-| % in a-mono- | character of 
and per cent of | on. _| bromnaph- 2V over | the disper- 
FeO. gr.=Tl. y=Na. r=Li.|  thajene. axis 6. | sion and of 
the double 
, a B y | refraction. 
Branchville. Giese GBA. oo | Gi 97 66° 257 001 
Salmon. Cesar FLO OLY oat: 66 5 65 13 p<v 
MeO—A-24G ir, =--- L612 .__. Go - 14 63 23 Positive. 
a=—a \b=c ¢c=b 
Branchville. gr. .... 1°682 _...| 64°55’ | 64° 16’| 001 
Light clove-brown.|y. 1°676 1°679 1°687 63 34 62 54 pu 
BeO—o47R \7- ---- 1674 ....| 62 10 Sh ae Positive. 
Pranenyitie. \g7. .... 168% ___- 59° 56’ 502 220% 001 
Light clove-brown|y. ---- 1682 __..| 56 59 5G 40 aca 
mate pIsh cast. |7 <..-. 1678 ...- 54 32 53 24 Positive. 
FeO=13°63% 
2E over axis b 
7 1691 1°692 1°698 ae 28" 2s Gor | 001 
Grafton, N. H. ” a=a =C ¢=6 | Positive. 
Light blue or , : : ° ° Uniaxial. 
Peer ee 688, 1692, ° Positive. 
FeO =26'58% 1683 1-684 1-691; 25° 28” | 15° 3’| 100 | 
r. nt 
a—cb—a) ¢—o Positive. 
Rabenstein. AO ae About 120°) 100 
Light -gray with eee (Otc $52 or 60° over p<cu 
greenish cast. _ aoe on cor@g | Negative. 
FeO=35 054 ac b=a ¢=6 
The material from Rabenstein was unfortunately poorly 
adapted for optical work. Numerous sections were cut par- 
allel to the best cleavage, 001, but none was sufficiently trans- 
parent to admit of an accurate measurement of the divergence 
of the optical axes by means of the ordinary axial angle appa- 
ratus. By examination with convergent light under the micro- 
scope it was seen that the sections were at right angles to the 
acute bisectrix, and that the plane of the optical axes was 100. 
By using the most ‘transparent section and the little apparatus 
devised by Klein,* for examination with polarized light in a 
liquid whose index of refraction is about like that of the min- 
eral, it was found that the divergence of the optical axes 2Va 
was about 60° with dispersion ev; hence 2V over the erys- 
tallographic axis }, as given in the previous cases, would be 
* Sitz. Ber. Akad. Berlin, xxiv, p. 435, 1891; also Groth’s phys. Kryst., 3d 
edition, p. 750. 
Am. Jour. So1.—Tsi1rp Series, Vou. L, No. 299.—NoOVEMBER, 1895. 
26 
