422 The American Naturalist. [May, 
A modification of the microchemical method for determining ironin 
minerals is given by Lemberg.” It consists in producing Turnbull’ 
blue from the ferrous sulphide precipitated on the mineral in question. 
Alurgite and Violan from St. Marcel.—Among the minerals 
from the Manganese mines of St. Marcel, Piedmont, alurgile and violan 
haae always excited considerable interest because of their rich color 
and their variety. The alurgite was described by Breithauptas a deep 
red mica. Penfield" has recently obtained a sufficient quantity of the 
material for study. He describes it as monoclinic in crystallization 
and micaceous in habit. Its cleavage plates are flexible and somewhat 
elastic. It is biaxial with 2 E,, — 56° 32’ (average) and its dispersion 
is ¢ > v, but often plates show a uniaxial optical figure, due, as the 
author supposes, to twinning. The mica is one of the first order, andin 
spite of its dark color, its pleochroism is very slight. Density = 2.836 
—2.849. H==3. Composition: 
SiO, AlO, FeO, Mn,O, MnO MgO K,O NaO H,O Tod 
53.22 2119 122 87 18 6.02 11.20 34 5.75—=900 
In the formula H R, (Al OH) A1Si,0,,, R = K and Mg OH. Alurgié 
is thus a distinct species, which is more nearly allied to lepidolite hes 
to muscovite, although it is a potash mica. The alurgite is as 
with a jadeite composed largely of a soda-rich pyroxene that is pleo- 
chroic in pale rose and pale blue tints. Its density is 3.257 3.882, 
and composition (mean of two analyses) : 
SiO, ALO, Fe,O, Mn,O, MnO MgO Ca,O Na,O K,O Ign r 
54.59 9.74 11.99 1.06 .58 5.03 7.24 9.32 .24 OT 
corresponding to Na R(SiO,), in which R= Al, Fe”’,Mn”. The mineral 
occupies about the same position in the pyroxene group asgi f 
does among the amphiboles. In composition it agrees oa 
with the chloromelanite from Mexico analysed by Damour. alysed 
For purposes of comparison with this pyroxene, the author an : 
a specimen of violan whose density was 3.272 — 3.237, with this 
. K otal 
SiO, Al,O, Fe,O, Mn,O, MnO MgO CaO Mn,O K,O im a 
5394 1.00 86 88 .36 186.63 23,80 1.22 05 =" 
The figures indicate a mixture of the diopside, jadeite and acmite me | 
“ Zeite d. deuts. geol. Ges., 1892, p. 823. 
"8S. L. Penfield. Amer. Jour. Sci. SUVA, p- 
u : 288. te No. 30: 
Bull. Soc. Min. d. Franc, IV, 1881, p. 157. Cf. also foot-note 
