Account of some new Vesuvian Minerals. 251 
pears in form of estremely small, straight ea crys- 
tals, of red colour, which are placed in the interstices of oth- 
er extremely small crystals, capillary, contorted saat brown. 
Nitric acid, when cold, does not attack breislakite, but when 
heated, reduces it to a most impalpable yellow powder, which, 
on cooling, is precipitated. In the flame of a lamp, this 
down is heated esa alteration, but before the blowpipe, 
it melts into a black enamel. 
Locality. ‘The bivalents lines the small bubbles found 
in the lava of Scalla, where it is accompanied by muriate of 
copper, pseudo-nepheline, and some small yellowish-white 
undetermined crystals. It is also found in cavities in the la- 
va of Olebano, near Pozzuoli, and is there distinguished by 
its reddish-yellow colour. 
Wollaston alone has analyzed this mineral ; according to 
him, and our own observations, it consists of silex, alumine, 
and a little iron, 
HUMBOLDTILHITE.* 
(Umboldilite.) 
Specific characters 
Geometrical Pharacters. The primitive form is a right 
rectangular prism, with a square base—the plane G being te 
B nearly as 20 to 39. 
Physical characters. Sp. gr. is 3.104—it scratches Se 
is translucent in mass, transparent in thin lamina—has a 
vitreous lustre in some crystals—fracture vitreous and con- 
choidal—but the fragments are irregular acuminated pieces. 
The colour is brown, tending slightly to egg ea in 
some crystals. small splinters have no colour 
Chemical characters. Pulverised and treated with nitric 
acid, it is converted into a perfect jelly. 
Exposed to heat, the point becomes rounded without 
changing color, and preserving its transparency, but before 
have chosen the word Umboldilite, to otis ie it a Humbold- 
tine, ‘aden in honour of Baron Hu mboldt,) which la s been given 
‘by Sig. Rivero, a young ! Peruvian, to the suboxalate of it iron, on, ound n Bohe- 
znia, with strata of bituminous wood, at 
* 
