Crystallized Muriate of Silver

This valuable specimen was brought me by its owner John Williams jun., Esq., who had it from Mexico mine in Cuthbert parish, Cornwall, found at about eight fathoms depth. The crystals in this substance are always very small, but in the present specimen are very easily determined; they are cubes and cubo-octaëdrons, either regular or elongated, and more or less deeply truncated. They are in some parts distinct, in others more or less confusedly huddled together, others filling the hollows in smaller varieties, or confluent in them. The peculiar texture of this mineral has given it the apt name of Horn-Silver: it is, however, peculiar to itself, and rather like softened horn, inclining to waxy: hence it may be indented by the finger nail, and takes the impression of any equally hard substance. It feels less hard or harsh than horn in cutting, and receives by the instrument a waxy polish. The crystals break easily with an irregular conchoidal fracture, not unlike Quartz, but perhaps in a blunter manner, and shining like the common surface. They vary in colour from a light olive to a dark green , and are rather more transparent than wax, which otherwise they much resemble. The specimen gives out an odour like that sometimes inhaled on the sea coast. The matrix is chiefly cubic Sulphuret of Lead and brown Ochre. My specimen, which has the elongated crystal No. 3, is principally composed of Quartz with some spiculæ of Carbonate of Lead.

The Corneous Silver Ore is composed, according to Klaproth, of

Its specific gravity is from 4.745 to 4.084. Brisson says 4.7488.

The Silver may be very readily extracted from this ore on Charcoal, with the addition either of Iron or of a fixed Alkali, by the blowpipe, when a fœtid odour passes off, and leaves the Silver in a globule or globules^*.

It is found in France, Spain, Norway, Hungary, Bohemia, and Siberia, and also in America; but Cornwall is the only county in England, or indeed in Great Britain, in which it is found. This mineral was once very abundant there, and the Silver produced from it has been wrought into a tea-table equipage, &c.

We are the more obliged to Mr. Williams for the use of the present specimen, as it clearly elucidates the form of the crystals, which were scarcely determined before.