Fluor-uvite and Tremolite from Bush Farm, St. Lawrence County, New York
Contributed by: Michael Crawford
Date: Sep 5th, 2025
Locality: Reese farm, Gouverneur, St. Lawrence County, New York, USA (See on Mindat)
Size: 8.5 x 10 cm
Description:
A specimen of brown fluor-uvite (CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3F ) and tremolite (Ca2Mg5(Si8O22)(OH)2) from the Bush Farm, St. Lawrence County, New York. Mindat calls this location the Reese Farm although several other references and specimen labels call it Bush Farm or Dale Bush Farm. The farm is closer to the town of Richville, but it occurs in Gouverneur township and both locations are used on specimen labels. Labels that accompany specimens can contain various combinations of these location names.
The fluor-uvite is found in pockets of Precambrian metasedimentary calc-silicate rocks in contact with the Grenville Marble.
The fluor-uvite fluoresces pale yellow only under shortwave UV illumination. The emission spectrum is a very broad peak. Manganese is a likely activator for the pale yellow fluorescence. The broadness of the peak suggests that it is composed of several narrower peaks. The complex chemistry and structure of fluor-uvite might allow manganese to replace magnesium and calcium with different coordination with surrounding atoms. This different atomic coordination might create different peaks that make up the broader peak. A second activator could also cause the broader peak.
The activator of the tremolite fluorescence that causes the bluish white fluorescence is unknown. There are patches of purple fluorescent calcite in midwave + shortwave image. This calcite fluoresces only under midwave light and it is activated by manganese replacing calcium.
Summary of luminescence responses:
Fluor-uvite (Mindat) (RRUFF)
- Fluorescence under Shortwave (255nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: White