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Identity HelpVuggy rock

6th Oct 2016 00:16 UTCAndy Young

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Here is a rock I found in the water off of a South Haven, MI beach. My question is about the colored crystals in the vugs. They are not cleaning off easily, and I wonder whether they are sand crystals stuck inside, or crystals growing on the white minerals? Also in the fourth photo has a white coating down inside the vug, sediment or mineral? Finally, how do I test any of these tiny minerals? Sorry for the lack of scale, the vugs are thumbnail size, the small crystals are visable only with a loupe.


Thanks!

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6th Oct 2016 00:18 UTCAndy Young

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6th Oct 2016 01:02 UTCBob Harman

ANDY, I believe you have found small sedimentary type quartz geodes in limestone matrix. These are occasionally found in this part of Southwest Lower Michigan.


In your first series of photos, the small pepper like spots on the quartz crystals could be either goethite, marcasite or tiny pyrites as all 3 of these mineral are commonly found on the quartz crystals of Midwest geodes. Don't try to remove them as they are a true part of your geode specimen. As to testing them.....not easy....you can try picking several off the quartz, but that will damage your geode; best leave them in place and just add the mineral id possibilities that I have given you.


In your last pictures, I see corroding water worn calcite upon the quartz crystals. Also very common in geodes and corroding forms are what is usually found in long opened geodes.


Hope this helps. CHEERS.....BOB
 
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