Identity Helpoffshore Keweenaw calcite locality
Folks:
I’m looking to get some advice on the appropriate locality for a calcite found in the Keweenaw District, out in Lake Superior. The label I have reads, “offshore from Seven Mile Point, west of Ahmeek, Keweenaw Co.” It was supposedly found in a clay pocket, circa 1985. Pictures are below; the cores are dull, crud-included calcite scalenohedra with overgrowths of clear, highly-lustrous calcite. (First picture shows the overall look, second highlights the partial overgrowth of clear calcite.) Longest dimension in the below specimen is 6.3 cm.
My first choice is Sevenmile Point near Ahmeek, but there is also Seven Mile Point Beach near Eagle River. Neither lists calcite as a known mineral. I’m just wondering whether this piece rings a bell for anyone who can add more details on the find. Thank you!
Cheers,
D.
Don,
Fabulous Copper Country calcite!!
I'm surprised calcite isn't listed for Seven Mile Point. It is found there, but mostly as a fracture filling mineral and not in crystal form like what you have. Because of the amount of fissures that extend offshore from the Keweenaw, it would not surprise me that the label is correct. Many of the fantastic copper crystals from the bottom of Lake Superior (including the ones found in the Laker Pockets) are found in clay pockets and seams.
Another interesting tidbit is that the updated Mineralogy of Michigan states that "In the 1970s, some remarkable tabular, butterfly twinned crystals to 6 cm were collected from a calcite vein cutting across sandstone on the shore of Lake Superior midway between Sand Hills lighthouse and Seven Mile Point." It's quite possible that your specimen is related to this occurrence. 
Paul:
Thank you for weighing in. Calcite is one of those minerals (like quartz) that probably can show up just about anywhere. I'm just wondering if anyone had heard of or run across this particular find.
I think the butterfly calcites you reference are associated with Five Mile Point, as there are a few nice examples shown for that locality. I own a clear little TN from that locality -- not one of the twins, unfortunately -- but it's a very different habit from the piece I pictured above.
Cheers,
D.
