1895.] Mineralogy. 563 
General Notes. 
MINERALOGY.’ 
Origin of the ‘‘Pflockstruktur’’ of Mellilite.—The “peg 
structure” (“ Pflockstruktur,” “ Structure en chevilles”) of mellilite is 
one of its most constant characteristics. This structure has been at- 
tributed to original glass inclusions in the mineral. Gentil’ has re- 
cently made a careful microscopic study of this mineral from the local- 
ities of Mte. Vultura, Capo di Bove, Hohenstoffeln (Héhgau), Hoch- 
bohl, Palma (Canaries), and Rachgoun (Algiers). He concludes that 
the “peg structure” is due to products of decomposition of the melli- 
lite, of which the most common is a honey-yellow hydrated substance 
which gelatinizes readily with hydrochloric acid. It has a lower index 
of refraction and a weaker double refraction than mellilite. The 
double refraction is so weak as to be hardly appreciable in the small 
thicknes of the “ chevilles” and hence was supposed by Rosenbusch to 
be isotropic. In the mellilite of Vultura and Capo di Bove it is, how- 
ever, easily made out. In the mellilites from Hochbohl and Palma the 
decomposition has proceeded farther, producing a zeolite, probably 
mesotype. This process Gentil likens to the serpentinization of oliv- 
ine. The direction of development of the “ chevilles” (normal to the 
base) is a direction of easy decomposition and is, in some cases, at least 
one of weak cohesion. 
Blowpipe Coatings on Glass.—Goldschmidt* has proposed the 
use of a simple device for holding a small glass plate (an object or 
cover glass) or a mica lamella on the surface of a stick of charcoal, so 
that the blowpipe coatings are deposited on the glass or mica. It 
is thus possible to remove them and examine under the microscope or 
by chemical methods. The fusibility or solubility may be tested and 
the material is adapted to study by the methods of microchemical an- 
alysis. By use of sodium sulphide as a reagent, colored precipitates 
are obtained as follows: From arsenic, cadmium yellow; antimony, 
reddish-yellow; lead, molybdenum, tellurium, and copper chloride, 
1Edited by Dr. Wm. H. Hobbs, University of Wisconsin, Madison, Wis. 
* Bull. Soc. Franç. Minér., xvii, pp. 108-119. May, 1894. 
* Zeitsch. f. Kryst. xxi, pp. 329-333, 1893. 
