Ely greenstone (nonfiction)
Ely greenstone
Ely greenstone boulder
Minnesota Geology Monday: No telling what will turn up in a local farm field! This is a boulder of pillow lava – basaltic lava erupted underwater giving resulting in bulbous, rapidly chilled masses. The rock has been metamorphosed to a greenstone, with epidote replacing the pillows and a mix of darker chlorite and other minerals replacing the sediments between the pillows. Pillow lava in our region, such as exposed around Ely, MN, are records of submarine volcanic eruptions about 2,700 million years ago.
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Jim Cotter on Ely Greenstone
Ely Greenstone is one of these great ancient rocks that we have so many of in Minnesota. It's over 2.7 billion years old. It's a volcanic rock. And it occurs in and around Ely.
... So the unique thing about it, though, is even though it's ancient, it still has a lot of features in it. It hasn't been all that beat up by geologic history. So it's just a great rock to study.
... Ely Greenstone is a lava flow, a lot like the lava flows in and around Gooseberry Falls. So it has that nature to it, but it's undergone some metamorphic processes. And that has transformed some of the minerals into a group of minerals that are more green-like. And so it has a kind of greenish-black tone to it. The minerals are chlorite and epidot.
