Rock On!

January 29, 2010 7:51 AM

Can you identify this mysteriously green rock?

I usually pick up interesting rocks when I go fishing. This one was found in a river in Colorado. It is really green and very smooth (is was in the river). Anyone know what this is? $2.5 million worth of rare jade? Radioactive "Homerite"? Or, just a green rock?

posted by ecorrocio to science & nature (29 answers total)

Kryptonite! Sorry.

I think it's just algae staining a regular old rock.
posted by amro at 7:54 AM on January 29, 2010

I don't know about the algae - this thing looks green through and through.
posted by ecorrocio at 7:56 AM on January 29, 2010

I should also note that I almost never see greenish rocks in Colorado rivers. Pale green at best.
posted by ecorrocio at 7:57 AM on January 29, 2010

this may be of help.
posted by vivelame at 7:58 AM on January 29, 2010 [1 favorite]

(ie, there's more to minerals identification than a good picture.. But you don't necessarily need a chemist set either!)
posted by vivelame at 7:59 AM on January 29, 2010

It's something in the Serpentine group, aka "fake jade."
posted by Cool Papa Bell at 8:15 AM on January 29, 2010

It was in the river? I'll bet you $2.5 million that it's just a normal rock covered with algae.
posted by Cat Pie Hurts at 8:18 AM on January 29, 2010

Serpentinite. . .Cool Papa Bell is correct.
posted by Danf at 8:21 AM on January 29, 2010

Yeah, looks like algae to me too. The right side of the bottom picture is just brown. Can you break it open?
posted by DU at 8:26 AM on January 29, 2010

If you do break it open, be careful, cause if it is serpentinite (of which I am not convinced) I believe it contains asbestos.
posted by amro at 8:27 AM on January 29, 2010

amro, I was absolutely sure that the last word of your sentence was going to be "snakes". *needs more coffee*
posted by Cat Pie Hurts at 8:53 AM on January 29, 2010 [3 favorites]

It's algae.
posted by thylacine at 9:09 AM on January 29, 2010

Came here to suggest some type of serpentine rock. As I recall, those types of rocks are pretty soft, so one way to tell is to take a knife to it and see if you can scrape off anything. And they do indeed contain asbestos. Or take a rock hammer to it and see what it looks like inside.
posted by elendil71 at 9:21 AM on January 29, 2010

Some of the worlds finest nephrite jade, comes from Southern Wyoming; can you scratch it with steel?
posted by hortense at 9:27 AM on January 29, 2010

Green SHALE. Common.
posted by Oireachtac at 9:51 AM on January 29, 2010

Hey!! I had planned to place a question about a darker green rock I found 20 years ago next week (as I wasted this weeks question on orchids...) This is a super cool AskMe!!



ecorrocio, I have picked up quite a few of those same type of stones on hikes in SoCal. I'm looking at one right now. Can't remember if I got them on the beach, mountain, or high desert (probably beach or mountain, leaning beach.)


As per Cool Papa Bell and his guess in the Serpintine group - I pulled up pics for Bowenite (a variation of Antigorite) and Garnierite.


You can see samples pics on this mineral page. The Bowenite pic is in the "A's" list, under Antigorite (variation: Bowenite.) Scroll down further to see the Garnierite.

Rember, I have those rocks? Notice how the Garnierite sample on this list is from the Riddle Mine in Oregon? If you googles this mineral, pics of more translucent rocks come up, but these are from different places in the world. Our rocks look like the one from the Pacific Northwest, which is near where our samples are from.

Anywho, if you look at the samples from the Riddle Mine, I imagine if those were polished (like ours from tumbling in river beds, etc.) the red veins/deposits would look just like our stones.

That's my best guess.

Thanks for asking this question!

And look out for my Yosemite rock mystery, next Wednesday!
posted by jbenben at 10:23 AM on January 29, 2010

Do a scratch test on tile for a cross-check on the guesses here.

And -
If you do break it open, be careful, cause if it is serpentinite (of which I am not convinced) I believe it contains asbestos.

amro is overconcerned. Asbestos kills through LONG-term exposure. A couple strands in the air from cracking a rock open is about as lethal as looking at a mercury thermometer.
posted by IAmBroom at 10:31 AM on January 29, 2010

Well, I took 2 years of mineralology and I can't tell from that picture. It looks like it could be anything covered in algae. You definitely need to look at a fresh surface, so break a corner off and look at that. And chances are it's a rock, not a mineral, there are probably a bunch of minerals in it.

Most of the serpentine I've seen is pretty fibrous looking and really soft. I can't see it surviving in a river for long.
posted by piper4 at 10:34 AM on January 29, 2010

I would say algae, if you don't want to break it open you can try a soak-and-scrub process with bleach to see if the green comes off...but algae can stain/embed pretty darn thoroughly.
posted by anaelith at 10:43 AM on January 29, 2010

If you do break it open, be careful, cause if it is serpentinite (of which I am not convinced) I believe it contains asbestos.

It's not that all serpentine is asbestos, it's that the mineral serpentinite can be present in a fibrous habit, which makes it harmful. In my experience the areas where there is asbestos material it is usually in thick bands and is obvious. It also doesn't weather like the samples here. I'm not saying there isn't any asbestos material in there, just that I don't think it's likely.

That said I think it is even more unlikely becuase it's not serpentine but chert.
posted by Big_B at 10:48 AM on January 29, 2010

amro is overconcerned. Asbestos kills through LONG-term exposure. A couple strands in the air from cracking a rock open is about as lethal as looking at a mercury thermometer.

And this is absolutely incorrect. There is no minimum exposure to asbestos necessary to have problems. One fiber can kill you. You are sort of correct with regard to the long time issue - but only in the sense that it takes >20 years before the problems start showing up.
posted by Big_B at 10:50 AM on January 29, 2010

Sorry - should've put these all in one comment.

A scratch test is going to be the answer to figuring this out - Chert is hard and cannot be scratched with a nail. Serpentine is easily scratched.
posted by Big_B at 10:52 AM on January 29, 2010

Asbestos kills through LONG-term exposure. A couple strands in the air from cracking a rock open is about as lethal as looking at a mercury thermometer.

As a safety professional, I have to agree with that statement. We all have asbestos lodged in our lungs, arguably from walking down the street inhaling air which as sloughed off asbestos from brake linings.

The people who get mesothelioma and asbestosis are the ones who inhaled mass quantities of it, and their families, who inhaled mass quantities from the clothes of the worker.

Having said, that, it's good to avoid exposure, and I would bag that rock before taking a knife to it, then wash my hands.
posted by Danf at 1:36 PM on January 29, 2010 [1 favorite]

Asbestos kills through LONG-term exposure. A couple strands in the air from cracking a rock open is about as lethal as looking at a mercury thermometer.

As a safety professional, I have to agree with that statement. We all have asbestos lodged in our lungs, arguably from walking down the street inhaling air which as sloughed off asbestos from brake linings.

I didn't mean to sound alarmist in my original comment, and we can start touting qualifications if you want (I used to be an a licensed asbestos contractor in the State of California), but the fact remains that the overall evidence suggests there is no safe level of asbestos exposure. I'm not arguing that more exposure = more likely to cause problems, or vice versa, but saying a couple of strands in the air is as lethal as looking at a mercury thermometer is not backed up by studies of risk associated with asbestos material.

I'd really like to know the results of the scratch test so we can determine what this rock is though. Also the approximate location found might be helpful.
posted by Big_B at 6:56 PM on January 29, 2010

Asbestos is found around serpentine but serpentine is not asbestos, I have seen veins or bands of asbestos in serpentine but they are very obviously different materials.
posted by hortense at 8:29 PM on January 29, 2010

Thanks for the input folks. To answer some above:

Algae: At first I didn't think so... but on close examination this might be possible. I'll try the bleach scrub. Interestingly, it was the only rock in the area like that. Really stood out. I would have thought there would have been others nearby if it were algae.

Hardness: This is a very hard rock - not scratchable with a metal implement, will not fragment with a solid impact.

Polished very smooth by water, but seems to have innate smoothness--- I'm leaning toward Garnierite or Chert- green (is there's such a thing), or algae stained Chert.
posted by ecorrocio at 2:33 PM on February 1, 2010

What river in Colorado?
posted by hortense at 8:39 PM on February 1, 2010

Shoulda been the Green River... but alas, it was the Blue. BUT, it was below Green Mountain Reservoir. That did not occur to me until just now. Wonder why it's called Green mountain?
posted by ecorrocio at 11:57 AM on February 2, 2010

Tumble it for a week with tempered glass and a tiny bit of chrome oxide to refine the natural polish.
posted by hortense at 11:09 PM on February 2, 2010