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March-April 2015

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Letters

POLYHEDROIDS

I read with great interest John White's article on polyhedroids in the May/June 2014 issue (pages 275–278). He wrote only about quartz polyhedroids, and I was reminded of the calcite polyhedroids I had found years ago. This was the first time I had seen anything in the literature about this unusual mineral form. I went digging through the boxes of minerals in my back room and opened up the box of minerals from a backpacking trip into Dunn Peak near Barriere, British Columbia. Dunn Peak is a granite intrusion, and I had collected mostly small smoky quartz and feldspar from miarolitic vugs in boulders. One granite boulder contained a pocket of flat layered calcite, some of which had formed polyhedroids as described by Mr. White. I kept a few of these weird calcites and have included photos of three. I have collected calcite in many different environments and have never come across any other polyhedroids, so maybe the unusual occurrence of calcite in the granite resulted in their formation. Maybe they were formed from a fragment of limestone caught up in the granite when the intrusion cut through the surrounding sediments. In any case these are interesting specimens. Hopefully, someone will be able to explain how they formed.

Two views of a calcite polyhedroid, 9 × 4.5 × 5.5 cm, from Dunn Peak, Barriere, British Columbia, Canada.

Two views of a calcite polyhedroid, 9 × 4.5 × 5.5 cm, from Dunn Peak, Barriere, British Columbia, Canada.

Calcite polyhedroid, 8 × 5 × 2.5 cm.

Calcite polyhedroid, 9 × 7 × 3.5 cm. Both are from Dunn Peak, Barriere, British Columbia, Canada.

MANGANESE MINE AND BEARS

That was a great article about the Manganese mine in Keweenaw County, Michigan, in the September/October 2014 issue (pages 498–513)! While at Michigan Tech University (MTU), I worked on a senior research project at the Manganese mine, which Tom Rosemeyer generously cited in his article. It was sad to see what the loggers have done to the rock pile–another collecting locality soon to be gone forever.

While reading the article, I was trying to piece together the timeline for my involvement at the mine. I remember the hole at the bottom of the trench was open in about 1988 or 1989. I went in it once. I remember because I had walked up the road to the mine from Lake Manganese to collect, and when I saw that there was an open hole at the bottom of the trench, I walked back to the car to get my underground gear and then back to the mine, a distance of just over a mile. I went in by myself but didn't collect much. I clearly recall the thick calcite vein on the wall and the manganese mineralization in the vein.

On a subsequent visit in the fall of 1990 or 1991 (after I had graduated from MTU), I again stopped by the mine. I scrambled down into the trench, and the hole was still open. Not having any underground gear, I wasn't planning to go in. It was generally my habit to toss a rock into a hole to see how far it was open and if there was water present. Well, I didn't do it this time—luckily. When I got to the bottom of the trench and looked into the dark opening, I clearly saw a furry head with eyes looking out at me! I was no more than about 10 feet from a bear, and if I had tossed a rock, I would have hit him right on the nose and really made him mad! Needless to say, I got out of there rather quickly. I'm pretty sure he didn't follow me out of the trench, but I didn't stick around to find out.

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