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Identity HelpBlue and White Mystery Rock

17th Jan 2020 05:58 UTCJulie Farnsworth

I'm not sure where this originated, but I got it from the Gem and Mineral Club in Globe, AZ.  It was ID'd by them as marble, but I pretty much doubt it.  The blue is almost navy, the brown has a green tinge, and both can be scratched by a knife.  The white part won't take a scratch.  (My hardness tools are at school, so I'm going old-school.  Vinegar doesn't cause a reaction to any part of this rock.  It doesn't appear to fluoresce under UV.  I think it would be interesting to explain this to my middle school students, if anyone has any ideas! I have a couple more pictures, and the blue does seem to go through the entire rock

18th Jan 2020 01:29 UTCJosé Zendrera Expert

Julie, this is a rock (mix of small mineral grains) that con be hardly identified only with a photo and some inaccurate data. If you need reliable information about it a serious petrographic study is necessary or find an expert of the zone who can recognize it.
Another possibility sometimes very useful is to know the exact locality of origin, look for it in USGS geological map and read captions and geological map memory.
Maybe that's why you had not many answers...

18th Jan 2020 02:10 UTCJulie Farnsworth

Jose, thank you!  I know rocks are very difficult to identify (especially when location isn't known), but it's always worth a try!  On the positive side, I found this site which is going to be very helpful in my (fairly) new job of teaching middle school science.

18th Jan 2020 03:13 UTCPaul Brandes Manager

Welcome to Mindat, Julie!

Apologies for not responding earlier, but José is correct. It is sometimes difficult to identify a mineral with proper information strictly from a photo. A rock can up the difficulty at times by ten! I believe what's throwing off a lot of people from responding are the results of your testing. This would be a fantastic candidate for a thin section to be made and viewed under a petrographic microscope.

You said you had a couple more photos; could we please see those?

18th Jan 2020 04:09 UTCJulie Farnsworth

Yes, I know rocks and crappy camera pics, along with little clue about origin (I assume SW US since the Rock/Gem club is in Arizona and there is a layer of desert patina on a side)  Unfortunately, I live in Nowhere, so technical opportunities are limited.  I may cut another piece off, and see if a paleontologist friend has any ideas.  I've stumped a whole group with some purple fossils I've found :)

I'm curious but it isn't all that important.  It'll be interesting to slice it up.

18th Jan 2020 13:22 UTCEd Clopton Expert

At least we can agree on the "not marble" conclusion based on the negative vinegar test.  That's something.

Just curious--what part of Nowhere do you live in?  I may have been there, or close by  ;-).

18th Jan 2020 14:45 UTCJulie Farnsworth

I'm up on the Mogollon Rim in the White Mountains

21st Jan 2020 22:22 UTCGail Spann Manager

Welcome Julie !!! Will you be going to the Tucson Gem and Mineral show? 

18th Jan 2020 14:50 UTCRolf Luetcke Expert

Been to a couple of those, one maybe in Michigan, if you get my "drift".
Another friend had a mineral from "the" North Pole, only to have me tell him it was from Alaska, again a place with same name.
Welcome also to mindat, great place to explore minerals but rocks are a bit more difficult, I just posted a "rock" and asked about it since I have it displayed with no information at all, hope someone recognizes it.  Have fun with the rocks you find, suggest finding someone in your area that knows rocks and minerals or your closest rock club.

21st Jan 2020 21:39 UTCGregg Little


Might I give you another approach.  Since those who you sourced the rock through, and we here at Mindat are having trouble with the rock type, might you be further ahead to source a better rock (ie better mineralized, coarser crystals, typical matrix or rock type, etc.).  I am sure you could find common examples of granite or gneiss or pegmatite or even bedded material like sandstone or limestone.

If we here are having difficulty with identification, it is probably insurmountable for you; in other words a poor teaching example.
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