Hydrozincite & calcite from Franklin
Hydrozincite {Zn5(CO3)2(OH)6}:  FL Blue SW
Calcite {CaCO3}: FL Red-Orange SW

I found this specimen at the Buckwheat night dig on November 5, 2005... quite a nice find!  I actually trimmed it down after I got it home, and luckily it came out alright.  Sometimes when you try to trim blocky calcite, it cleaves right through the middle of the rock and ruins the specimen.  Fortunately that didn't happen.

Hydrozincite forms when zinc minerals, particularly sphalerite or zincite, are exposed to water for prolonged periods.  The brightest hydrozincite at Franklin seems to come from the alteration of sphalerite, not zincite.  I don't know for certain why this happens, but I have a theory.  You see, it's not really the sphalerite itself that determines the quality of hydrozincite;  it's the host rock.  Franklin sphalerite typically occurs in a carbonate-rich matrix (calcite or dolomite), while the zincite is often in a dense franklinite matrix that's largely devoid of calcite gangue.  As you can see from the formula for hydrozincite, this mineral can't form unless carbonate ions are present.

Back to the night dig.  It was great fun, though all 3 hours went by in the blink of an eye.  There was a family from Hampton, NJ who showed up but didn't have their own UV lamp, so I had them stay around me on the dump.  The young man helpfully carried my bucket;  I already had my hands full with a 4-lb mini-sledge and a UV lamp.  Anyhow, I don't think he minded lugging the bucket around, since I found some good minerals for him too.  I was using an old Mineralight from the 1960's, connected to a SuperBright battery and a 300W power inverter which whirred away in my backpack.  The SuperBright was temporarily out of service.

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