Analcime

specimen number:
2062325

location:
Keweenaw Peninsula, Michigan, USA

description:
Very fine thumbnail for the species from this area, a large well-formed lustrous slightly translucent crystal of analcime measuring 2.3 cm across set perfectly up on matrix. In great condition.

The Keweenaw Peninsula, situated in the Upper Peninsula of Michigan, is a globally famous native copper district where analcime occurs as a notable secondary mineral rather than a primary industrial target. Geologically, the peninsula is composed of the Mesoproterozoic Portage Lake Volcanics, a thick sequence of basaltic lava flows interbedded with conglomerates, where low-grade hydrothermal metamorphism filled gas vesicles and fractures with zeolites and related minerals. Analcime typically crystallized within these basaltic amygdules alongside native copper, calcite, epidote, and prehnite during the cooling and alteration phases of the volcanic strata. Formal industrial mining in the district began in the mid-1840s, focusing strictly on native copper extraction across hundreds of mines, including major operations like the Calumet and Hecla. While copper mining peaked during the late nineteenth and early twentieth centuries and largely ceased by the late 1960s, analcime was consistently encountered throughout this century-long period of active extraction as miners breached mineralized pockets within the basalt.

Questions about this specimen?
Send an email or call us: 314-341-1811.