We say we're in the Granite State, but actually New Hampshire's rocky foundation is less than half granite. What are those other rocks? And how did they get there? For answers we turn to Granite Geek David Brooks. He's a reporter for the Concord Monitor and writer at GraniteGeek.org. He spoke with All Things Considered host Peter Biello.
(This transcript has been lightly edited for clarity.)
So what, if not granite, is underneath us here in this so called Granite State?
So called Granite State, them's fighting words. So we're talking about the bedrock here. This is the stuff that's kind of underneath the soil, somewhat less than half of it is granite. Most of the rest is called schist which is a term for a metamorphic rock which is a rock that started as something else and kind of got squished and heated and turned into schist.
So how did it get here?
As far as geologists have been able to understand, in the last couple of billion years what is now New Hampshire has been part of no less than four different plate collisions. Quick lesson, looking back, you remember we all sort of float on a bunch of plates that are kind of on top of, underneath the crust and we’re all floating around and occasionally run into each other. They sometimes do things like make the lava appear in Hawaii.
And four different times there's been one plate or another that's collided with, gone under or gone over another plate under what is now New Hampshire. And these have left lots of different kinds of rock behind in the bedrock. Some of it is melted igneous rock, some of it is sort of heated and squished metamorphic rock. And so all these have been wrapped over each other and mushed and mashed over billions of years it’s created a real mess I guess you could say.
So there's a lot of schist in New Hampshire but granite is not that kind of rock, it’s an igneous rock, right?
Right, granite is an igneous rock. It's been basically melted and cooled and melted until it sort of becomes largely uniform and then cooled again.
Why are we talking about this this week?
We are talking about this this week entirely because Lee Wilder, who is the outreach coordinator for the state’s geological survey, pointed out an error that I had made. A month or two ago I was writing about Mt. Kearsarge and I mentioned, “I'm up there on the granite boulders.” And he said “Well, actually Mt. Kearsarge isn't granite. It's schist.” And I said “Huh?” And that led to a conversation and that led to this column saying the Granite State really doesn't have as much granite as we thought.
Well, I think a lot of kitchens don't have as much granite as they thought. If you think you have granite countertops, they’re actually not granite, they’re something else.
Most of them are not granite. That is correct. Because granite, because it's an igneous rock, it's all been melted. It's kind of uniform in appearance. Here in Concord we're familiar with Swenson which is the granite quarry up on Rattlesnake Hill. It's by far the biggest granite quarry in the state. And this famous Concord granite, almost all of it goes to curbing. If you think of gray granite curbs, that's Concord granite. Very uniform, neat, but it's not all that exciting to the eye in your kitchen.
So most granite countertops that you buy in kitchens are not in fact granite. They are almost certainly schist because schist is a mix, it’s a metamorphic, it's been squished, it’s been heated, a lot of different rocks you still can see them, it's got neat patterns, it looks really cool.
One of the things I found interesting about your column this week is that the granite between towns in New Hampshire can be so different. There's the Concord granite and then there's also Conway granite.
Yes that's correct and there are others that I don't know. And it's a function of what other minerals were present in small amounts at the time that the melting occurred. And so it's strictly a function of what happened 150 or 500 or 2 billion years ago.
You also write that the type of granite that made up the Old Man of the Mountain was partly the reason why it crumbled. What was it made out of?
It had a relatively large amount of feldspar which is another mineral that goes into granite. But it weathers comparatively quickly and so there was too much feldspar in the wrong places. The Old Man was actually five different ledges that sort of looked like a profile from the side. It was eaten away by rain over time and if it hadn't had so much feldspar it would still be there.
And finally David, after researching all this, do you feel like Granite State is a misnomer?
We should absolutely be the Schist State or maybe the Gneiss State, which is another type of rock. No, of course we should be the Granite State. And I put that to Lee Wilder, that was sort of the joking reason I talked to him. I said “Is this a misnomer?” He said “No, of course not.” Geology isn't everything. Granite has been one of our defining industries over time, above and beyond the metaphor for personality. He's perfectly content with Granite State and therefore so am I.
The Granite State we shall remain. That's David Brooks. He's a reporter for The Concord Monitor and the writer we had thought about renaming the Igneous Rock Geek but it lacks the je ne sais quoi of GraniteGeek.org.