Melanocerite-(Ce) — Cardiff Uranium Mine, Cardiff Township, Haliburton County, Ontario

A black, vitreous rare-earth borosilicate from one of the storied uranium properties of the Bancroft area. The Cardiff Uranium Mine was originally explored for fluorite in 1943 before Cardiff Uranium Mines Limited began uranium development in the 1950s, working veins that cut amphibolite, syenite gneiss, and marble — host rock that also produced calcite, fluorapatite, chondrodite, and lokkaite-(Y).

Melanocerite-(Ce) here occurs as dense, glassy black masses with a characteristic conchoidal fracture, often intergrown with smoky quartz — material that is notably heavy in the hand even where quartz makes up a significant share of the mass. As a cerium-dominant member of the melanocerite group, its structure carries measurable radioactivity from associated thorium and uranium, consistent with the mine's broader radioactive mineral suite. Well-formed Cardiff material is uncommon on the market; most specimens in circulation today trace back to decades-old mine-dump collecting before the site was rehabilitated.

Species: Melanocerite-(Ce)
Locality: Cardiff Uranium Mine, Cardiff Township, Haliburton County, Ontario
Radioactivity: Present — handle and store per standard radioactive mineral practice
Approx. activity: