| 550 General Notes. [June, 
= Mineratocicat News.—A. Lacroix! hasanarticle inthe “ Comp- 
tes Rendus” on the optical properties of some minerals which are 
without crystal forms. In it he affirms the discovery by Des 
makes it appear orthorhombic, with a pleochroism in three shades 
of brown. The plane of the optical axes is æ P x, the bisectrix 
being positive and normal to this, which is the direction of easy 
cleavage. Withamite, xantholite, scoulerite and chalilite are iden- 
tified respectively with piedmontite, staurolite and thomsonite, of 
which the latter two are but impure varieties ——Some interest- 
ing manganese minerals are described by Weibull? from the 
Wester-Silfberg mine in Dale Karlien, Sweden. A manganese 
magnetite gave on analysis 6.27 per cent of MnO. It is un- 
f crystallized and is associated with masses and grains of mangano- 
. calcite. The massive variety contains 6.98 per cent of MnO an 
ae the granular mineral 24.32—24.89 per cent. A careful examina- 
tion of Igelstromite* (2Fe,(Mg) SiO,+Mn, (Mg) SiO,) proves it 
to be orthorhombic, with the optical axes in the plane of the 
base and the æ axis the negative bisectrix. Pleochroism : b 
\ 
In polarized light these crystals are seen to be composed of 
twinned lamella with the orthopinacoid the twinning plane. 
plane of the optical axes is the plane of symmetry, and the double 
refraction is negative. The pleochroism is marked, ¢ = dirty 
oe brown, Bite brownish-yellow with a green tinge, i= yellow 
white. Absorption, ¢>6> a. An analysis of a pure variety 
gave: 
SiO, FeO MnO MgO CaO AlO; #0 
49.50. 30.69 8.24. 8.10 2.02 69 a 
_ In the same article the author reports the result of a re-pram 
tion of the Knebelite of Dannemora. This mineral jerge mee 
_ columnar masses of black to blackish-gray individuals, with tet 
_ cleavages, one parallel to the faces of a prism of 50° 6’, very S 
fect, and the other two parallel to the brachy and macro Pl wel 
_coids. A parting perpendicular to the three cleavages betas Bits 
Comptes Rendus, cit, Mars 15, 1886, p. 643. 
< Mincralogische und Petrographische thik ungen, vit, 1885, P- 108. 
Cf. Zeitschrift f. Kryst., viir, p. 647. 
 *Geol. Foren. Förħand], vi, p. 504. 
