Acanthite (after argentite), Gersdorf, Frieberg, Saxony, Germany

We have a number of historical specimens formerly in the collection of Sarah Topham and Prosper Williams. This wonderful old-timer, for example, dates back to the 1800s and comes with a long line of historical labels. Somewhat telling of this specimen's age are the "argentite" labels. Mineralogy, as a science, has now determined that argentite is the high-temperature (> 173 C), cubic version of silver sulfide (Ag2S) whereas acanthitie is the stable, but orthorhombic, version of the same elemental composition. Thus, this wonderful little specimen is correctly a pseudo-cubic acanthite after argentite; meaning this piece started its life over 173 C, grew into a cubic crystal but cooled below this temperature but retaining its morphology. Complicated but fun to learn about. Note the specimen is on a green wax mounting, probably also from the 1800s. From Gersdorf, Frieberg, Saxony, Germany. Dimensions: 0.5 x 1 x 1 cm ON HOLD