16 July 2012

Hooper Garnet Mine

Posted by Jessica Ball

Recently, I finally trekked across NY state to the Adirondacks and visited the Gore Mountain area, home of several garnet mines. Now, these aren’t like the garnets I was showing in my Bancroft photos. These are HUGE. Garnets as big as your fist. The two best places to find them are at the Gore Mountain Garnet Mine (which charges an entrance fee and by the pound for what you take out), and the Hooper Mine, which is no longer in operation BUT is also free. Being grad students, my friends and I went for the free option. (The garnets at Gore mountain are, admittedly, bigger, but there is a limit to how much rock even I am willing to drive back across the state.)

The Adirondacks are composed mainly of metamorphic rocks (gneisses and other) and a core of igneous intrusives, which are all part of a Precambrian Grenville basement similar to the one I described in my Bancroft posts. The rocks formed around a billion years ago, but the mountains themselves were uplifted only 5 million years ago – and the uplift is still ongoing. In the last hundred thousand years or so, glaciations have also sculpted the landscape, eroding and smoothing it and leaving deposits of material all over the Adirondacks dome.

The Hooper Mine opened in 1898, but closed soon after when the owner (Frank Hooper) realized he couldn’t compete with the crystals coming out of the nearby Gore Mountain Garnet Mine (apparently he went to work for the owner of Gore Mountain, too). The garnets were originally mined for abrasives, and the mines in this area are so famous that the garnet is New York’s State Gemstone. Now the Hooper Mine is on state land, which means collecting is allowed. To reach it, you pass through the grounds of the Garnet Hill Ski Lodge and resort. They get a lot a visitors for the mine, so they put together a nice little walking map and are happy to direct you there. (It’s polite to stop and let them know where you’re headed!) The hike is short, about half a mile uphill, and ends at a great outcrop of garnet-bearing amphibolite overlooking Thirteenth Lake.


View Hooper Garnet Mine in a larger map

Beautiful scenery at the top of the hill

Darn big garnets!

Not only is the outcrop full of lovely garnets, it has a ton of glacial striations!

Glacial striations in the outcrop

Glacial geomorphology and metamorphic petrology. Yum!

The mine itself is quite overgrown, but there is plenty of talus on the north slopes (and also some bouldering potential if you’re into rock climbing, although there’s a lot of loose rock and I’d be very┬ácareful).

One of the clearer slopes. Minimal rock-breaking is needed - there's so much loose material already!

The amphibolite is pretty gneissic in places

It also seems like some of the garnets have been rotated, although it's hard to determine a sense of shear.

It’s easy to spend hours here turning over (and breaking) rocks, but there’s always time for a little fun.

Nants ingonyama baghiti baba....okay, it's not a lion, but I don't know the Zulu word for rock.

If you look carefully, you can find pockets of what (might) be skarn: garnets in greenish-white masses of small crystals. These garnets are much more likely to be euhedral and unfractured; the larger garnets, which come out of the amphibolite, have tons of cleavage plains and it’s quite difficult to find intact examples.

Finding your favorite garnet takes a bit of scrambling, but it's worth it!

More of the mine

The mine is quite easy to get to, but be sure to bring sturdy boots, gloves, serious rock hammers, and plenty of bug spray and sunscreen (and snacks!) If you’re tired of roasting yourself in the mine, the Hudson River is also nearby and there seem to be a lot of rafting companies running trips.