Acanthite on Quartz
Chispas Mine, Arizpe,
Arizpe Municipality, Sonora, Mexico
8.3cm tall x 6.9cm wide
Acanthite, from Mexico, has always been on collector’s lists of must-have species. Mexico has been the source of the world’s finest acanthite specimens since the late 19th century. Acanthite is a common species mined around the world, but well-developed geometric crystals are rare. Acanthite is primarily made up of the element silver. Before the 20th century, acanthite was often known as argentite. It was eventually proven that argentite and acanthite are the same species, but only acanthite is stable at below 173 degrees Celsius.
This example is particularly desirable, having exceptionally sharp acanthite crystals on a matrix of terminated quartz crystals. The acanthite crystals have grown on the opposite side of the quartz terminations – appearing like a cloud city floating on an icy glacier. At the very top are spiky elongated acanthite crystals which are slightly hollow. These unusual crystals might be what is known as “primary” acanthite. These would have grown at lower temperatures, and not ever gone through the phase of initially growing as argentite and then cooling down into what we know as acanthite. Equally as curious is that as you move down the specimen, the remaining crystals are more likely those that moved through this process and could be called paramorphs of argentite – now acanthite.