Yooperlite cobble from the Holocene of Michigan, USA. (~7.6 centimeters across at its widest)
"Yooperlite" is a rockhound term for beach clasts of syenite containing orange-fluorescing sodalite. They are found along gravelly beaches of Lake Superior, principally along the northern shoreline of Michigan's Upper Peninsula (= "U.P." - people who live there are "Yoopers").
Syenite is a potassium feldspar-rich, quartz-poor, coarsely-crystalline (phaneritic), intrusive igneous rock. Other minerals occur with the feldspar, such as dark-colored pyroxene and amphibole, and often nepheline.
Yooperlite is a sodalite-bearing syenite. Sodalite is a feldspathoid mineral having the chemical formula Na4(Al3Si3)O12Cl - sodium chloro-aluminosilicate. It is often bluish-colored (see:
www.flickr.com/photos/jsjgeology/albums/72157714493738277), but in yooperlite, it's light- to grayish-colored. Under ultraviolet light (black light), the sodalite in yooperlite rocks glows bright orange (see pictures elsewhere in this photo album).
Published research (Lauglin et al., 2018) indicates that yooperlites can be sourced to the Coldwell Alkaline Complex, along the northern Lake Superior shoreline in Ontario. The Coldwell Complex includes sodalite syenites having orange-fluoresceing hackmanite, a variety of sodalite. Pleistocene glaciers likely eroded Coldwell Complex rocks and deposited them on the American side of Lake Superior.
Geologic provenance: likely center 2 of Ontario's Coldwell Alkaline Complex, late Mesoproterozoic, 1.108 Ga
Locality: unrecorded / undisclosed site along the southern shore of Lake Superior, Upper Peninsula of Michigan, USA
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Reference cited:
Laughlin et al. (2018) - A new find of fluorescent sodalite from Michigan's Upper Peninsula. Mineral News 34(5): 1-3. (
www.yooperlites.com/img/Yooperlite_Sodalite_Discovery_Pap...)
