Datolite

specimen number:
1791265

location:
Ojibway Mine, Keweenaw Co., Michigan, USA

description:
An attractive cut and polished datolite half nodule. Good color on this one.

The Ojibway Mine, located in Keweenaw County, Michigan, was established in the early 20th century, with major development beginning around 1906 under the guidance of geologist Lucius L. Hubbard. Despite significant capital investment and deep shaft sinking targeting the Ojibway and Kearsarge amygdaloid lodes, the mine struggled with low commercial returns and closed intermittently before halting operations permanently. Geologically, the site sits within the Keweenaw Peninsula's Precambrian Midcontinent Rift system, characterized by a sequence of ancient basaltic lava flows and interbedded sedimentary rocks. Its mineralogy is defined by hydrothermal alteration assemblages, featuring native copper and native silver alongside characteristic secondary minerals such as calcite, prehnite, pumpellyite, and various zeolites filling amygdaloidal cavities and fracture zones.

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