What are they?
These stones were all found in Minnesota, so they were probably abraded
and deposited by the Pleistocene glaciation. The stone in the lower
right is a sandstone (layering, aligned vertically, is evident); we
don't know what the whitish partial coating is. The stone in the upper
right appears to be a quartzite and when struck it rings like a quartzite.
It shows evidence of many collisions with other rocks. We can't identify
the rock in the upper left, but it's some type of igneous or plutotonic
rock.
Certainly, some meteorites that fell thousands to millions of years
ago might eventually have ended up in a glacial moraine, river, or
ocean where they got abraded by other rocks until they obtained shapes
like this. To our knowledge, however, there are no known meteorites
that have that history. Most meteorites are unstable in wet environments.
They chemically weather to sand, clay, and rust before they physically
weather to the shape of beach stones.
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