
828 The American Naturalist. [September, 
tetragonal melanophlogite. Analysis of these gave SiO, = 93-2 per 
cent., SO, = 5.7 per cent.- This substance loses twelve per cent. of 
its weight on heating, while the tetragonal mineral loses six per cent. 
- treng declares that the mineral does not contain sulphuric acid, since 
it yields SO, only when treated with an oxidizing agent. Whether the 
sulphur is in the form of free sulphur or of an organic sulphide, could 
not be determined by him. The crystals, according to this author, are 
bounded by %0% and %02, and are probably pseudomorphs of opal 
and quartz after some unknown mineral. A little more than a year 
ago the nodular rose-red eudtalite of Magnet Cove, Arkansas, was 
described by Hidden and Mackintosh. Recently crystals of the sub- 
stance have been investigated by Dr. J. F. Williams, These are tabu- 
lar transparent or translucent rose-colored or crimson bodies traversed 
by cracks in all directions. They are hexag@mal with a: ¢ = 1: 2.1174. 
OR, wP2, R, —%4R, —2R appear on one crystal, and on another 
occur in addition —8R, R. 4R and —3{R°. The density varies 
between 2.804 and 2.833, and the double réfraction is positive. It is 
one of the youngest of the constituents of the eleolite-syenite in which 
it occurs. The negatively refracting eucolite, of about the same compo- 
sition as eudialite, appears in brownish-yellow crystals in the same rock. 
In it a cleavage parallel to OR is quite pronounced. OR, R, — 1R, 
œR, and œP2 bound its crystals. Its specific gravity is 2.6244—-2.6630, 
and its hardness 5-5.5. He thinks it may be an altered eudialite. 
The zinc-bearing rhodonite from Franklin and Sterling, N. J., has been 
reinvestigated by Pirsson.!® The crystals are usually tabular and 
elongated, parallel to oP. The new planes 2P=, 4Pa and 4P 
were observed. The axial ratios, calculated from the best measure- 
ments obtained, are: g: 6: ¢ = 1.078: 1: .6263, a = 103° 39; 
R = 108° 48’ 30”, y = 81° 5s’. The cleavage is prismatic, and the 
extinction on the basal plane is 54° from the edge OPaPy. Since the 
crystallographic constants and the extinction of the mineral differ so 
slightly from those of rhodonite, it seems that the isd aia action 
of the zinc is but slight. Composition : 



SiO, FeO -Z200 MnO CaO MgO 
46.06 3.63 7.33 34.28 7.04 1.30 
corresponding to RSiO,. Upon data collected during the course of 
many analyses of wraninite from American and foreign localities, Mr. 
1 Amer. Jour. Sci., XXXVIIL., 1889, p. 494. 
15 Ib., Dec., 1890, p. 457. 
16 Ib., XL., Dec., 1890, p. 484. 





