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Geologists! Identify this rock!

zhen_roguezhen_rogue Registered User regular
Hello all:

This rock came from a relative, but we have no idea where it was found originally. It could have come from mars for all I know.

The rock is approximately the size of a large grapefruit, a human brain, or a big head of cauliflower. You get the idea.
It's rather heavy, feels very solid - I doubt there's a hollow/cavern inside, or if there is one it's small.

It seems to be a nodule of some sort, and I can see minor quartz crystals embedded in some of the "bumps".
It could be agatized, or it could be a geode of some sort - or, it could be unremarkable inside. Who knows.

My initial google searches lead me to possibilities of a Howlite Nodule, or possibly a Datolite Nodule.

Before I drop cash on a lapidary specialist to try and identify and/or slice the rock, I thought i'd see if any of you could offer more info.
Thank you in advance! Please let me know if I can answer any other questions.
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    VeritasVRVeritasVR Registered User regular
    Looks like an unpolished and uncleaned cluster of quartz.

    CoH_infantry.jpg
    Let 'em eat fucking pineapples!
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    DarkPrimusDarkPrimus Registered User regular
    Geodes tend to be even more boring on the outside, the ones I've seen anyway.

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    Donovan PuppyfuckerDonovan Puppyfucker A dagger in the dark is worth a thousand swords in the morningRegistered User regular
    That is dwarf bread.

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    Blake TBlake T Do you have enemies then? Good. That means you’ve stood up for something, sometime in your life.Registered User regular
    It looks like hand polished limestone.

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    bowenbowen How you doin'? Registered User regular
    Blake T wrote: »
    It looks like hand polished limestone.

    Yeah, definitely looks like something with calcium in it.

    not a doctor, not a lawyer, examples I use may not be fully researched so don't take out of context plz, don't @ me
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    dlinfinitidlinfiniti Registered User regular
    Well first of all, its a mineral

    AAAAA!!! PLAAAYGUUU!!!!
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    MrDelishMrDelish Registered User regular
    It might be an animal. Perhaps a vegetable.

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    halkunhalkun Registered User regular
    I Man I don't know what it is, but it looks delicious!

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    InvisibleInvisible Registered User regular
    It looks like size, shape, color and texture of the rocks my grandfather used to line his flower beds. I couldn't tell you their name, but when smashed open they had "crystals" inside. So I'd go with quartz.

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    Dunadan019Dunadan019 Registered User regular
    It looks like a chunk of marble

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    CaedwyrCaedwyr Registered User regular
    A simple test you could try (may or may not succeed) is putting a few drops of 0.1 M Hydrochloric acid if you have it, or white vinegar if you don't onto the surface of the rock and seeing if it fizzes. If it fizzes, then it's got some calcium.

    If you are looking at a piece of limestone, then cutting it open will probably get you more of the same. As mentioned upthread, it doesn't look like a geode which would be worthwhile cutting in two to see what in side. On the other hand, if you are looking to turn this rock into bookends or some other new thing, then you still might be able to make something nice looking if you cut it and polish the surface.

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    Natas_XnoybisNatas_Xnoybis Registered User regular
    Caedwyr wrote: »
    A simple test you could try (may or may not succeed) is putting a few drops of 0.1 M Hydrochloric acid if you have it, or white vinegar if you don't onto the surface of the rock and seeing if it fizzes. If it fizzes, then it's got some calcium.

    If you are looking at a piece of limestone, then cutting it open will probably get you more of the same. As mentioned upthread, it doesn't look like a geode which would be worthwhile cutting in two to see what in side. On the other hand, if you are looking to turn this rock into bookends or some other new thing, then you still might be able to make something nice looking if you cut it and polish the surface.

    What Caedwyr said: drop some hcl on it and see if it fizzes, or try and scratch a piece of glass with it. if it fizzes you are looking at something like calcite etc., if it scratches glass it is quartz or harder. Wish I could be more help. I took mineralogy in hmm 1995, and "use it or lose it" has kicked in big time

    I hate Computers
    GIS is evil
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    CycloneRangerCycloneRanger Registered User regular
    It looks like a quartz nodule similar to these:

    http://www.agslapidary.com/brainnod1.html

    Possibly even from the same locality (there are references on the 'net to collecting similar specimens from Arizona, e.g. http://www.greatsouth.net/rockcollectingbook/collecting_geodes_payson_arizona.htm)

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    zhen_roguezhen_rogue Registered User regular
    Wow!
    Those quartz nodules look to be spot-on. The color, texture, and arrangement are dead ringers.
    That would likewise explain why upon close inspection, I can see varying degrees of translucent quartz crystals throughout the "bumps".

    Thanks to everyone who commented and researched, it's very much appreciated.

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    ComradebotComradebot Lord of Dinosaurs Houston, TXRegistered User regular
    Aye, definitely looks like quartz. The HCL test may help clarify that, as others have suggested.

    Though not 100% possible to tell without me being able to actually handle it myself. It definitely looks like a quartz nodule, but you'd be surprised by how many rocks/minerals can look like one another and be completely different things or look absolutely nothing alike and yet are essentially the same thing.

    But in all likelihood, its probably quartz. Though I've seen dolomite and dolostone that slightly resembles this thing (and to test for either of those, make a small scratch and then apply HCL to the scratch).

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    zhen_roguezhen_rogue Registered User regular
    I found a gemologist/rocksmith who said he'd be happy to use his lapidary saw on the nodule to see what's inside.
    I won't be able to visit him for a couple weeks, but will reply here as soon as I know (if the thread isn't already closed).
    Thanks again for all the help!

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    CaedwyrCaedwyr Registered User regular
    Comradebot wrote: »
    Aye, definitely looks like quartz. The HCL test may help clarify that, as others have suggested.

    Though not 100% possible to tell without me being able to actually handle it myself. It definitely looks like a quartz nodule, but you'd be surprised by how many rocks/minerals can look like one another and be completely different things or look absolutely nothing alike and yet are essentially the same thing.

    But in all likelihood, its probably quartz. Though I've seen dolomite and dolostone that slightly resembles this thing (and to test for either of those, make a small scratch and then apply HCL to the scratch).



    In a minerology class we had a mineral identification quiz where there were 25 samples of sphalerite, and each one looked different. That was a mean test, but a good way to learn how similar things can appear and how different minerals that are the same can appear..

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