Super-sulphuret of Arsenic; Orpiment

This is one of the most beautiful of Minerals, and at the same time one of the most difficult to imitate; its lustre is very great; its transparency too is great, whence the reflection from between the laminæ is transmitted in a way that gives it a semimetallic appearance wholly beyond the feeble powers of the Artist to give an idea of.

The colour I consider as a perfect yellow when seen in the mass; if it be transparent to a considerable depth, the intensity of the colour gives it a redness approaching to orange, I have observed the same in Gamboge and other bright yellows; indeed the colour is so clear that the least stain is noticed by every observer. The Realgar in crystals I consider as a pure red, but its powder is orange; thus the Native Orpiment and Realgar may be quoted as examples of two primitive colours, and the Realgar in powder as an example of orange. The artificial Orpiment has always an orange tinge, and is variable, and King’s yellow, which is sometimes free from the red, is too pale as well as too variable to be considered a standard for yellow. When pure it is the same as the Native Orpiment in powder, which is much paler than when in the mass^*.

Native Orpiment is found in Hungary, Transylvania, China, and several other places; it is sometimes accompanied by Realgar, Arsenical Iron, Iron Pyrites, Quartz, &c. In the specimen figured it is accompanied by granular Iron Pyrites. It adorns Mr. Heuland’s collection.

Thenard found this substance to contain, Arsenic 57, and Sulphur 43. Perhaps future experiments upon crystallized specimens of Realgar, and pure ones of Orpiment, may prove one to contain twice the quantity of Sulphur that the other does.