Lithified Detritus, long-time commenter and friend at ETEV, responded to ye olde beach rocks post by sending in beach rocks that, quite frankly, left me burbling incoherently. You know that feeling you get when you see something so awesome all you can do is make vaguely syllable-shaped noises and then attempt to breathe? Yeah, that's what happened. Covet. Covet these rocks.
Anyway. Rocks and their story, by our own Lithified Detritus. Images and words belong to him. The puddles of saliva are mostly mine.
You asked for beach rocks. As you wish...
This is from Presque Isle Park, in Marquette, MI. It's a lovely place, with awesome beach rocks:
The origin of these cobbles is close by - this is serpentinized peridotite of the Mona Formation, Archean in age - 2.6 billion years. Here it is pretty metamorphosed and intruded. it includes pillow formations.
Higher up it is heavily weathered. More pillow lavas!
The pinkish stones in this shot are in fact sandstone, from the adjacent, and in fact overlying Jacobsville sandstone, a mere billion or so years old -dates are a little iffy.
The Jacobsville contains no fossils, but in many places shows mud crack, ripple marks, and raindrop impressions. It is widely used as a building material in the U.P.
Pretty beach rocks!
That's it. I am booking a damn flight to Marquette, Michigan. Who's got a couch I can crash on?
For those of you wishing to send me their beach rock beauties, you can send 'em on to dhunterauthor at gmail dot com. I've seen your comments on combing and anticipate awesomeness. Bring it!
The views expressed are those of the author(s) and are not necessarily those of Scientific American.
ABOUT THE AUTHOR(S)
A confirmed adorer of the good science of rock-breaking, Dana Hunter explores geology with an emphasis on volcanic processes, geology news, and the intersection of science and society. Her home away from SciAm is Dana Hunter's Unconformity