Nancy Barber (nlbarber) wrote,
Nancy Barber

Rock origins

I've spent most of the evening Googling for more information on my countertop. Geological information, that is. There's more info out there now than there was last summer when I found the stone, or perhaps I'm just searching on different terms. However, there's still there's a gulf between the terms and names used by the "granite" companies and those used by geologists. And so far I haven't manage to leap the gulf and find a formation name for my countertops.

But for what I did find, or already knew...

The slabs were sold to me as "Black Amazon with Gold" granite. It is not a granite at all (though some of the pebbles in it are): it's a metaconglomerate. A conglomerate, fundamentally, is a bunch of large pebbles to cobbles that are glued together somehow, usually with something finer grained like a clay. If you take that conglomerate and subject it to heat and/or pressure (say by burying it under a few thousand feet of other sediments, or by having a tectonic plate collision squish the area up some), the rock gets metamorphosed into a metaconglomerate. You can see the big pebbles in the icon photo, and might be able to see that some of them are a little stretched out by the metamorphic process.

So, today's search uncovered that this is more commonly called "Marinace", and probably hails from the state of Bahia in eastern Brazil. There's a very popular variety called Verde Marinace, but that one is decidedly greenish and mine is not. Found one site that showed a picture labeled Nero Marinace that looks like mine, or other sites that just call it Marinace. What I'm not sure of is whether "Marinace" is a generic term for conglomerate (and/or breccia, which is the same sort of thing with angular pieces instead of rounded ones), or if there are specific suppliers of each and thus maybe a specific geologic formation they come from. Or maybe Marinace is specific to Brazil, but still encompasses a range of rocks.

One last tidbit is that the Verde Marinace is Precambrian age. Which may not tell me anything about my countertop stone, of course.
Tags: remodeling

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