176 
_Arsenical Iron with some light Quartz; the latter in red 
Feldspar with Quartz and Mica, in which are interspersed 
smallish scattered particles of Pyrites, and the Molybdenum 
is dispersed in little particles, mostly on one broadish face, 
of a natural crack; but on the other sides of the stone, 
which is about half an inch thick, there is not the least 
particle to be seen. It therefore appears extremely local 
and partial. At first sight it has occasionally been con- 
founded with Plumbago ; but its micaceous foliated texture 
distinguishes it; besides, the lustre is truly metallic, and 
its colour bluer. Its folia are rather easily divided ; it soils 
with less ease than Plumbago, and its mark is paler. It is 
bright in itself, and does not allow of being made brighter 
by scratching. I do not know that it has been found with 
determined crystals in Great Britain; I have, however, 
shown the form of the crystal proper to it. As we possess 
many things besides the few that I have published, that 
have been chiefly ascribed to foreign habitats, I shall be 
glad to add them to our list *. 
* T intend to form a Supplement to British Mineralogy by publishing 
such few as do not seem likely ever to appertain to our island; see Adver- 
tisement on the cover. 
