Fluoborite from Lime Crest
Fluoborite: fluorescent white to pale yellowish-white, SW

Fluoborite {Mg3(BO3)(F,OH)3} occurs sometimes as grayish, anhedral crystal grains in the Franklin marble. It can fluoresce whitish to whitish-yellow under SW UV.

This specimen came from the Lime Crest Quarry during a field trip in 1999 or 2000. Fluoborite from the marble quarries is typically associated with chondrodite / norbergite, phlogopite, pyrrhotite, arsenopyrite, and graphite. Side note: Some people have argued with the arsenopyrite I.D., but when you hit a pyrite-like rock with a hammer and it gives off a garlic odor, it means there's arsenic in it. (Careful, these fumes are also toxic.) Also, the mineral I tested was also not magnetic, even when pulverized and even when subjected to a powerful samarium-cobalt magnet. So I say it's arsenopyrite.

Some fluoborite has been found at the "fill quarry" at Sterling Hill, which has an outcrop of the Franklin Marble.

Fluoborite with good fluorescence seems to have been rare at Lime Crest Quarry, though we probably overlooked it. In daylight the grains are very, very easy to miss-- they blend in almost perfectly with the surrounding marble matrix.

Specimen is about 4 inches wide.

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