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Thread: Help Identifying A Rock

  1. #1

    Default Help Identifying A Rock

    Found two of these in a SC creek bed. This one is near basketball size and fairly heavy. Any ideas?



  2. #2

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    It looks like a chunk of lava that gathered up other rocks and stones while it was hot enough to mold them in but not hot enough to melt them. I have a chunk but it is black and it is extreamly heavy. My Guess

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    Member Tearbear's Avatar
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    Quote Originally Posted by Water_Gremlin View Post
    Found two of these in a SC creek bed. This one is near basketball size and fairly heavy. Any ideas?
    A petrified Yeti turd?
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    webmaster Michael Strahan's Avatar
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    Drusy quartz?
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    Supporting Member iofthetaiga's Avatar
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    Quote Originally Posted by Michael Strahan View Post
    Drusy quartz?
    I think so. Some flavor or another of druzy chalcedony type stuff. I have a couple pieces here that I collected where a sea bluff had collapsed onto a beach exposing it. Sometimes it can be REALLY spectacular inside.
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    Thanks for the info. However, I'm having a hard time finding a picture to cross reference as almost all pictures are of small trinket jewelry. I'll keep searching on my end, this is a good starting point.

    Is there any value to druzy Quartz of this size? How about large pieces? The second we found was a pig. 24" x 12" x 8" and at least 60lbs.

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    Supporting Member iofthetaiga's Avatar
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    Google images for "druzy chalcedony geode" and you'll find a few photos amongst the clutter showing the potential. Lots of it can be soft and chalky, and pretty unimpressive as far as crystalline structure goes, but some of it makes spectacular and complex geodes too. That 60# chunk could have lots of solid crystalline or agate type core material, which is what is used for all that gem stone type jewelry in the photos. You'd have to consult a real geologist (not me) to determine what the composition really is and what you might be able to do with it.
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    Quote Originally Posted by iofthetaiga View Post
    Google images for "druzy chalcedony geode" and you'll find a few photos amongst the clutter showing the potential. Lots of it can be soft and chalky, and pretty unimpressive as far as crystalline structure goes, but some of it makes spectacular and complex geodes too. That 60# chunk could have lots of solid crystalline or agate type core material, which is what is used for all that gem stone type jewelry in the photos. You'd have to consult a real geologist (not me) to determine what the composition really is and what you might be able to do with it.
    I concur. Looks and makes sense.
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    From the closeup it's clearly a piece of pumice. Explosive volcanic rock.

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    If this was a chunk of pumice, it probably would not weigh very much...he said it weighed about 60 lbs. If you know someone with a rock saw you could have it cut open and see what it looks like inside, that would help immensely in the identification. I would use a rock hammer as the last resort, just in case it may have some cool looking crystals inside.
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    More info about where it was found would help clear up the argument Teadybear made against it being pumice. Water_Gremlin, where did you find it?

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    Member Tearbear's Avatar
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    Quote Originally Posted by AKChester View Post
    More info about where it was found would help clear up the argument Teadybear made against it being pumice. Water_Gremlin, where did you find it?
    That's O.K. AKPester. Not an argument, I'm just stating facts...pumice is very lightweight. If Water Gremlin is a prospector, I doubt he'll want to give out his exact location, SC covers a pretty broad area.
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    Default Help Identifying A Rock

    Looks like a highly weathered silicic rock to me (igneous). Feldspars are weathering out producing the brownish pinkish Fe staining. Somewhere near the bottom of the granitic triangle as there doesn't appear to be a whole lot of quartz in it relative to feldspars, hence the vesicled appearance.

    Could have been some secondary calcite mineralization that is now weathering out and leaving the vesicles, but not necessarily.

    Looks cool, guessing it likely came from the talkeetnas.

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    Default Help Identifying A Rock

    Just a side not on the drusy quartz, that refers to an alteration which happens after the primary rock formed, and there are virtually unlimited variations because there are so many rocks with some quartz in them. Si02 a prettying amazing little molecule.

    Igneous rocks have primary minerals from when they first cool, (think a hard granite boulder where you can distinctly see the light and dark specks,) but also secondary minerals on many occasions when it's altered by hydrothermal fluids.

    From those photos it is hard to tell how much original crystalline minerals are present in the rock from a photo, and how much of what you can see is secondary alteration. That rock could well have gone through several secondary alterations that have changed it's composition over time, and just being in a mineral stream there may even be small patches of recently formed surficial crystals on it.

    Cutting it open with a rock saw would potentially expose a clean, not weathered surface that would tell you more about the parent rock and how much it has been altered.

    Value? There's a sucker born every minute. But I like to think every rock I pick up has value to me.

    While that rock stood out to you in that stream, quite possibly there are more that crop out in some uphill drainage or rock face. Could be miles away of course, have to think where the glaciers would have brought it from.

  15. #15

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    Thanks for the responses everyone. I will do some reading on druzy chalcedony geodes.

    I will add another picture to show the larger piece as well. I would be willing to cut the smaller of the two in half if I knew how.

    Someone on another forum said the outside could be tuffaceous with a quartz nodule center. The pictures that I've looked at of tuffaceous are very similar to the outside of the rocks I have.


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    Supporting Member iofthetaiga's Avatar
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    I'm going to vote against a tuffaceous rock, and stick with a solution/precipitation formation mechanism. To me, your rock's surface looks like a weathered silica/limestone chalcedony of some sort. Final answer.

    http://www.bwsmigel.info/lesson10/de.gem.formation.html

    You should take that into the university geology department for an opinion. Please do follow up if you get a definitive ID.
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    If you put a diamond tile saw blade on a worm drive skill saw and keep it moistened with water on a sponge you can cut through the rock, though it looks like the ~3" cut depth from both sides from a skill saw isn't quite going to do it but you could cut off decent sized chunk
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    First glance I'm thinking calcium carbonate. a great indication that gold or other precious metals may be nearby because it's usually formed near an old crack in the crust that carries other minerals. But, just my .02.
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    Its a Skipper, (get it"lol ) j/k

    I'm no geo, but I have seen that rock alot around alaska, just not that big. ( good find )

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    Member Steve H.'s Avatar
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    Travertine.

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