Hemimorphite

Hemimorphite from Mapimi, Durango, Mexico, measuring 68 × 47 × 44 mm and weighing 102 grams. A good cabinet piece from a district with few equals anywhere in the world for the sheer range of secondary minerals it has produced.

Hemimorphite is zinc silicate, Zn4Si2O7(OH)2·H2O, named for its hemimorphic crystal form, in which the two ends of each crystal develop differently rather than mirroring one another; it typically grows as fans, crusts or bladed sprays of bluish-white to colourless crystals in the oxidised zone of a zinc deposit. Mapimi is built around the Ojuela Mine, whose immense, deeply weathered skarn orebody has been worked since colonial times and has yielded an extraordinary diversity of secondary zinc, lead and arsenic minerals, Hemimorphite among them, as oxidising groundwater moved through the exposed sulfide ore over a very long period.

A Hemimorphite from this locality sits alongside Ojuela's far more famous Adamite, Legrandite and Mimetite as part of the same broad secondary-mineral story, and it is a worthwhile piece in its own right for anyone collecting the district by species rather than by its headline minerals. This piece carries a double provenance, the David Vince Collection and Capital Minerals.