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Discussion Starter · #1 ·
Hello all,

I collected some rocked from a local stream today. I have been hearing something about testing them with vinegar? Has anyone heard of this? how does this work?

Thanks,
 

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OK, first of all, my credentials - an MS in geology, complete with courses in geochemistry including groundwater geochemistry. Now - Limestone will fizz if you put vinegar on it. On the other hand, there is a common rock called dolostone, composed of calcium magnesium carbonate - the mineral dolomite - completely or for the most part. It does not fizz if vinegar is placed on it, and if cold hydrochloric acid is put on it still will not fizz very much. Yet it also will dissolve in water - not as fast as limestoe, but fast enough that you do not want it in your tank. There are a number of other rock types that pass the fizz test but still are unsafe. For instance, any rock that has sulfides in it is bad. This includes iron sulfide, better known as pyrite or fools gold. Some slate is OK, some isn't. Members of the granite family and the very similar gneiss are OK. If you are near a university with a geology department, run it by there - just call ahead, and 99% will be very happy to help. In fact, it neeed not be a professor, just a student who has taken petrology. Or send me a photo!
 

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Discussion Starter · #4 ·
I just poured vinegar on them and there is a very very light fizzed sound. I have to put my eye right up to the rocks.
 

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I found a geologic map of the Philadelpha area:
http://www.sas.upenn.edu/earth/new.html
It looks to me like the rocks could have come from an outcrop of serpentine, which would acount for the slight fizz. I would not put these in my aquarium, for sure. It is of course very hard to tell from a photo, but the rocks look like they may indeed be serpentine. A greasy feel would to them would be a clincher. As I suggested, a visit to a local university's geology department could clinch the matter, but I would err on the side of caution.

The map shows your town is probably in an area of slate or phyllite (which is a poorly metamorphosed slate, in between shale and slate) but these rocks do not look like slate at all. As far as I can tell, they are not granite or gneiss, either.
 

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Discussion Starter · #6 ·
Thank you so much for looking into that! I will do what you said. The community college is right around the corner.
 

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Discussion Starter · #9 ·
I grabbed these rockes from a local stream. They were in the water. I guess I just figured they would be safe...
 
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