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Posts Tagged ‘corundum’

Beneath Robillard Mountain

Craigmont is about as distant from the reach of the modern world as you are likely to get in the “near north”. Indeed it appears on the map as a substantial settlement but as you cruise up Boulter road you become aware of how far you really are, both geographically and culturally from the bustle of Southern Ontario.

Coasting over hills that stretch off greenish-blue into the summer haze it seems as though you are crossing into a time warp. Meadows are saturated with intense colour and high pastoral fields line the road, strewn with orange and yellow flowers. Beyond this lies the valley of the “Little Mississippi River”. Spike-topped conifers wander unbroken to the horizon and in hillside fields lazy cows watch disinterestedly at the crumbling demise of old log barns.

As a collecting locale, Craigmont is remarkable. Not only is the beauty unsurpassed but its minerals are spectacular. Corundum here is found in large euhedral (perfectly formed) specimens; lapidaries have been known to cut them into cabochons. In their book, “Rocks and Minerals of Ontario” the Ontario Department of Mines say that there are unusual curved mica crystals. Garnets, molybdenite, allanite, uranite, euxenite, magnetite, pyrite and hornblende also appear from time to time.

Blink and you just might glide past Craigmont. The inhabited part is now a private town. It exists as a cluster of houses, barns and sheds and around it the vegetables flourish in earthy rows.

Robillard Mountain is situated within sight of the present habitation; an impressive upheaval of rugged red rock. Some twenty separate excavations scar its slopes.

As a general rule most corundum is found in pegmatites and structures associated with nepheline syenites. In this area north of Bancroft the most abundant deposits (corundum) are said to be sandwiched between scapolite, nepheline andesine and a band of alkaline syenite.

I took a hike beneath the mountain to see the syenite from below.

More on corundum in Craigmont here …

Check out this abandoned mine in Cobalt ... Here

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finding sapphires in Ontario

This is what ruby and sapphire looks like in their rougher forms. They are hexagonal crystals, generally displaying a six sided shape and in the case of the cabbed ruby in the fore-ground, also showing some pretty obvious hexagonal zoning. Zoning indicates the placement of the rough crystal faces as the crystal grows. There is a continuum between corundum and sapphire, both are of the chemical formula aluminum oxide, its just the quality of the crystal that dictates whether it will be a gem or a mineral specimen.

I found the blackish crystal encased in calcite at the Faraday Hill road cut near Bancroft; only the tip was protruding from the rock and I roughly chipped it out and dissolved the calcite from it using Coca Cola.

The two rough reddish crystals are Mysore Rubies from India – not woth much at all and the cab is also from India, I bought it from Sahib for a couple of dollars – its way to opaque to be of much value but I liked the way it showed the zoning so clearly.

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