Campylite

The specimen is about 6 cm across. The crystals in the inset show the barrel shape moderately well.

Campylite is not a legitimate mineral name. It’s usually applied to a distinctive variety of mimetite, lead arsenate chloride, with rounded crystals that at least vaguely resemble barrels. The word is from Greek kampoúra, “bent,” because the sides of the crystals are bent outwards like fat barrels.

My example here, from a famous locality at the S'Ortu Becciu Mine, Donori, Sardinia, Italy, is about 6 cm wide. It was labeled mimetite var. campylite, but it seems that most or even all of this material from Sardinia, when analyzed, is pyromorphite, lead phosphate chloride. That’s not really a big deal, because there’s a complete series between pyromorphite and mimetite, varying from the phosphate to the arsenate end members, with all proportions in between. Without a careful chemical analysis, this should really be called “pyromorphite-mimetite series,” but “campylite” also still works because it describes a habit in a variety of those minerals.

Likewise, the bent-barrel shaped crystals called campylite are not well-defined absolutes but are based on the subjective view of anyone who thinks the appearance meets the criteria. The “campylite” form can grade into botryoidal forms like my specimen, and on to sea-urchin-like shapes and beyond to approach standard hexagonal prisms of pyromorphite-mimetite, even in the same specimen. But the barrel-shaped crystals are rather distinctive, relatively unusual, and pretty. They can be many colors from red and orange to green, brown, and more.

The barrel shapes are not exceptional in my specimen, and it should probably be called “botryoidal pyromorphite-mimetite series.” In places the specimen contains acicular (needle-like) clusters of lighter green pyromorphite, as well as a few standard sharp hexagonal prisms.

Campylite was described as a new mineral in 1841 by German mineralogist Johann Friedrich August Breithaupt (1791 – 1873) in his Vollständiges Handbuch der Mineralogie (Complete Handbook of Mineralogy). It was later discredited when the original specimens were shown to be phosphate-rich mimetite (that is, toward the pyromorphite end, but not as much as 50% phosphate), but really it isn’t strictly a chemical variety of mimetite, but just a crystal habit. Nonetheless the name persists among collectors for this habit and is usually referred to as “mimetite var. campylite” but it can clearly also occur in crystals with more than 50% phosphate, when they should be “pyromorphite var. campylite.”

The deposit at S'Ortu Becciu was probably known by Roman times, but despite abundant lead minerals, it held little silver or gold and was exploited minimally until the early 20^th century when lead mining developed the mine. It was still serving as an occasional specimen producer at least until the late 1990s.

Sardinia has had a long, complex geological history, including mountains formed during the Variscan or Hercynian Orogeny (called Alleghenian in North America). That mountain-building episode extended from the Devonian into the Carboniferous, broadly (in multiple episodes) the period from about 370 to 260 million years ago, when Gondwana (South America + Africa + India + Antarctica + Australia + Zealandia), Laurentia (the ancient core of North America), and Baltica (the core of Europe) all collided to assemble the supercontinent Pangea.

As blocks and slivers on the northern margin of Gondwana continue to collide with Europe, tectonic motions to accommodate the interactions of blocks like Italy, Sardinia-Corsica, and oceanic crust, opened the Tyrrhenian Sea east of Sardinia. Sardinia is highly deformed continental crust and the adjacent Tyrrhenian Sea is oceanic crust in a small back-arc basin (Malinverno, 2012, Evolution of the Tyrrhenian Sea-Calabrian Arc system: The past and the present: Rendiconti Online della Società Geologica Italiana, 21:11-15).

My specimen (cat. no. 1916) once belonged to Colorado mineral collector Dennis Uridil, and was handled by dealers Rocksmiths and Scot Rosenthal.