Chlorite

Chlorite is a name collectors know well: a group of over ten closely related phyllosilicate minerals, including clinochlore, chamosite, cookeite, and pennantite, unified by a micaceous, foliated structure and a soapy, greasy feel. Its name comes from the Greek for "green," and indeed most specimens range from pale to deep bottle-green, though the chromium-rich variety kämmererite shows a striking violet-pink instead. Chlorite forms in low-grade metamorphic environments, greenschists, phyllites, and hydrothermal veins, and it commonly grows with epidote, actinolite, quartz, and calcite.

Classic collector-grade chlorite comes from the Maderanertal in Uri, Switzerland, prized for its shimmering green coatings on quartz and adularia that produce ghostly phantom crystals. In the United States, well-formed crystals are documented from the Green Mountain Mine in Yancey County, North Carolina, while the Tilly Foster Mine in Putnam County, New York, is famous for unusual chlorite pseudomorphs after other minerals. Additional notable pieces come from Zillertal in Tyrol, Austria, the New Idria District in California, and classic Alpine-cleft localities across the Alps.

Though often dismissed as an ordinary green coating on more glamorous minerals like quartz, adularia, or laumontite, fine chlorite specimens, especially sharp pseudohexagonal crystals, rosettes, and colorful kämmererite plates, are genuinely sought after by systematic and thumbnail collectors alike. Its role as a diagnostic mineral of the greenschist facies also makes it a favorite teaching specimen for students of metamorphic petrology.