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Reference Question of the Week – 5/3/09

   May 9th, 2009

mystery rockThis question didn't come from a library patron - it came from my brother. He found a weird rock in his yard and emailed me pictures to see if I could help him identify it.

I don't know very much about rocks, but I looked through our rock identification books trying to match it to the pictures. I also tried looking online, and found lots of rock and mineral identification websites, but couldn't find anything that looked exactly like it.

It turns out, rock identification is more more involved than I would have thought. With plants, birds, trees, etc., a good field guide is enough. But with rocks, you need to determine the hardness, the composition, the luster, the cleavage, and more, and still an ID is not certain.

Since I was striking out, I did the only thing I could think of: ask someone smarter than me. I sent the photos I had to friends of mine who work as naturalists, and I posted the photos on PicAnswers.com.

PicAnswers.com is a question-and-answer website, but instead of just posting a question, you post a photograph of something you need identified. I had never used it before, but posting this this mystery rock was a perfect opportunity to try it out.

Only one person responded, but he identified it as Calcite, which is what my naturalists friends thought it was, too. Having the same answer coming from multiple sources is good, but when I looked up Calcite in our books and online, it doesn't really look like the rock my brother found - which shows why actually knowing what you're talking about is important.

If you've never used PicAnswers.com before, check it out. Some of the photos people post - everything from antique tools to skin blemishes - are bizarre but interesting.

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5 Responses to “Reference Question of the Week – 5/3/09”

  1. Mary Ellen Petrich Says:

    Did your brother try the vinegar test suggested by the U Wisc site?

  2. Brian Herzog Says:

    @Mary Ellen: He did, but he said it didn’t do anything. I asked a geologist friend and he said it might have failed because of impurities on the surface or in the crystals – frustrating.

  3. Sue Abrahamson Says:

    I emailed my geologist daughter (Nebraska) and forwarded a link to your photo. Here’s her response. Hope it helps.


    The rock might be beryl, but it is difficult to know. Beryl is usually hexagonal (which these crystals are), but without holding it I can’t know it’s specific gravity or its hardness. Also, beryl typically forms in rocks called pegmatites, and I’m not terribly familiar with the geology of Ohio, so I don’t know if there are any pegmatites in that region. I would suggest the person’s brother takes the rock to a University geology department if he wants a real answer.

    Sorry I couldn’t be more help!


  4. Auntie Nanuuq Says:

    I concur “Beryl is usually hexagonal ” or maybe a piece of calcite?

  5. Auntie Nanuuq Says:

    Try these links:


    Lustrous, white celestine crystals to 3.0 cm on limestone matrix. The crystals look hexagonal, but are in fact, parallel growth. They are FLUORESCENT and PHOSPHORESCENT! This undamaged piece was collected in the early 1980s by Henry Fisher from the Lime City Quarry and the locality is now closed. this very striking two-toned habit is unusual and was found only a few times around that period.
    Origin: Lime City Quarry, Wood Co., Ohio, U.S.A.
    Sample size: 11.5 x 9.5 x 6.0 cm”