called Tlie Jeffersonite. ^ 319 
the minerals which occur there. I shall merely state, that the 
minerals which we collected, include, besides the oxidule of Iron, 
Franklinite crystallized in regular octahedrons with truncated 
edges. Garnets of various kinds, and, among others, a black emar- 
ginated dodecahedral Garnet, analogous totheMelanite of Monte 
Somma, Chondrodite, the same variety as exists at Sparta, and 
also a new variety of the same substance, besides many other 
interesting minerals. 
The present communication is intended to make known a mi- 
neral, which an attentive examination, made by Mr Vamixem 
and myself, has induced us to consider as a new species. Our 
observations upon this mineral, made separately, and at a dis- 
tance, have led us to the same conclusion; and the analysis 
which I undertook at his request, has fully confirmed the con- 
clusions drawn from its mineralogical characters. The following 
description includes, besides my observations, those with which 
Mr Vanuxem has favoured me. For the results of the chemical 
analysis I alone stand answerable. 
This mineral has hitherto been found in lamellar masses, the 
largest of which does not exceed a pigeon‘’s egg, embedded in 
Franklinite and Garnet. 
It presents three distinct cleavages, two of which are consider- 
ably easier than the third. These cleavages lead us for a primi- 
tive form to a rhomboidal prism, with a base slightly inclined. 
The angles of the prism are 106° and 74°, those of the inclina- 
tion of the base are 94 ° 45 ' and 85 ° 15 '. There is another face, 
which makes with the vertical face of the prism, angles of 110° 
and 70°. I have likewise seen, in one instance, cleavages paral- 
lel to a rhomboidal prism of 116° and 64 °. I have also obtained 
cleavages under an angle of about 99 ° 45 ' and 80 ° 15'. I have 
not been able to trace the connection between these and the for- 
mer, but I am inclined to think, that they result from the com- 
bination of the two prisms just mentioned. I had hoped, as 
some of the cleavages have^a tolerable degree of lustre, to have 
been enabled to determine the angles by the reflecting gonio- 
meter, but all my attempts to that effect have proved unsuccess- 
ful. I have not been able to obtain a reflection from any one 
face. 
