480 LARSEN AND SCHALLERI CEBOLLITE 



MINERALOGY. — Cebollite, a new mineral. Esper S. Larsen 

 and W. T. Schaller/ Geological Survey. 



At several places, notably six-tenths of a mile southwest of the 

 forks of Beaver Creek near Powderhorn, Gunnison County, 

 Colorado, some of the melilite of the occurrence described in 

 the preceding paper is altered to a dull, compact, white to green- 

 ish, fibrous aggregate, which on microscopical and chemical study 

 proved to be a new mineral, for which the name Cebollite- is here 

 proposed. In some specimens the melilite is replaced by a fibrous 

 aggregate of cebollite with little else while in others bodies of 

 the vesuvianite-garnet diopside type of alteration are scattered 

 through the cebollite. In general the two types of alteration 

 appear to be distinct. Thin sections show that the cebollite is 

 in microscopic fibers, commonly arranged normal to the original 

 cleavage of the melilite, or in fan-like or arborescent aggregates. 



Physical properties. Cebollite has a hardness of about 5 and 

 a specific gravity of about 2.96. It fuses at about 5 to a clear 

 glass. On account of the small size of the fibers cleavage could 

 not be recognized. 



Optical properties. The mineral is white to greenish gray. 

 The fibers are very minute and the optical properties could be 

 determined only approximately. The indices of refraction as 

 measured by the immersion method are: a = 1.595 ± 0.003; 

 ^ = l.GO; 7 = 1.628 ± 0.005. The extinction is parallel and 

 the elongation is positive. The fibers are too minute to yield 

 a satisfactory interference figure but the mineral is biaxial and 

 positive. The axial angle could not be accurately measured but 

 2E is about 80 ± 10° and hence 2V is about 58°. The mineral 

 is probably orthorhombic. Cebollite may be identical with the 

 mineral described by Rosenbusch^ as an alteration product of 

 melilite and considered by him to be a zeolite. 



^ Published with permission of the Director of the United States Geological 

 Survey. 



2 Pronounced C6- voi- 'ite. From CeboUa Creek in whose- drainage the min- 

 eral was collected. As in the preceding paper, locations are with reference to 

 the topographic map of the Uncompahgre quadrangle, Colorado. 



' Mikroskopische Physiographic der Mineralien und Gesteine, I : 2, 4te Aufi., 

 p. 72. 



