NATIVE COPPER
ABOUT THE SPECIMEN
Copper skulls such as this one are formations exclusive to the Keweenaw Peninsula of Michigan, and formed when hydrothermally deposited copper grew around felsite that later weathered away and left behind these hollow casts. While most other copper skulls one can find are small, incomplete fragments; this one stands apart with its completeness and ideal form, reminding one of a medieval helmet. All around the surface is a fantastic patina and green growths of other copper mineralization, with fragments of felsite still embedded on the inside and outside. Truly a museum-quality example of these unique natural sculptures and, with all of the aforementioned attributes, possibly one of the finest ever found. This specimen was formerly in the celebrated precious metals collection of the late Dan R. Kennedy, a giant in the mineral collecting community. Comes with a custom engraved display base, which, oddly enough, displays the wrong locality name, mentioning the Homestake #4 Mine in Keweenaw County rather than the Centennial Mine in Houghton County (this typo may have been made due to the Centennial Mine being formerly owned by the Homestake Mining Company).
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Keweenaw copper mineralization is among the oldest on earth, radiometrically dated to roughly 1,047–1,060 Ma, deposited hydrothermally within the Portage Lake Volcanics - a thick sequence of Midcontinent Rift flood basalts interbedded with sedimentary conglomerates. Skulls formed specifically in the conglomerate lodes, where circulating copper-bearing fluids permeated the matrix and deposited native copper conformally around pre-existing rounded cobbles - predominantly felsite and other volcanic clasts - that subsequently weathered out over geologic time, leaving hollow or partially hollow copper shells retaining the precise shape of the original clast. The resulting forms are entirely unique to this district; no comparable pseudomorphic copper habit has been documented elsewhere. Wall thickness varies considerably, and the finest examples preserve sharp outer surface textures imparted by the cobble's original skin alongside occasional crystal development on interior cavity surfaces. Most recovered skulls are fragmentary, as the same weathering that removed the core tends to structurally compromise the copper shell; complete, undistorted examples of cabinet size are genuinely uncommon. The bulk of known material dates to active mining operations running from the mid-1800s through 1968, and because the conglomerate lodes are no longer worked, the supply is effectively fixed to what has already been recovered.