Sulphuret of Lead, or Galæna
- Div. 3. Crystallized.
The Galæna, or Sulphuret of Lead, is remarkably striking in this figure, not only because it is eight times repeated in stripes, but the coincidence of the opposite halves is peculiar; the outer stripes are nearly of the same width, and the next within them double, and those again nearer the middle are single, and nearly the same width, so that the whole together form eight lines in pairs. The substance in the middle of the specimen is Sulphate of Barytes, and the substance between the lines of Sulphuret of Lead is Carbonate of Lime; there is some Sulphate of Barytes on the outer sides.
The specimen came from Derbyshire, I know not in what position it was found, whether lying horizontally, perpendicularly, or obliquely: it, however, has been admired as a remarkable stratification by some, and as an example of a vein by others, instancing what Dr. Thomson says of a vein according to Werner, where it is understood as characteristic of a vein to have opposite sides alike, with the same or different substances often repeated. The lower pair of double stripes differ from the upper in this specimen, by having a more regular and equally bounded zigzag line between them.
The lower figure is Sulphate of Strontian from Bristol, bounded by Sulphuret of Lead.
We do not know that this has been before noticed, and it is very rare at present. The modification of the Strontian indicates a centre, and the crystallizations seem to meet in the middle somewhat in points; but whether this lined a cavity on the inside of a fissure or vein I know not, nor does it often happen that the workmen are very particular in this respect; but metals of some kinds may be said to indicate veins or lodes, which are nearly the same thing.