Sphalerite and Calcite from Balmat, New York
Contributed by: Michael Crawford
Date: Jun 13th, 2025
Locality: Empire State No. 4 Mine, Balmat, Fowler, St. Lawrence County, New York, USA (See on Mindat)
Size: 7 x 10 cm
Description:
This specimen consists of sphalerite and calcite from the 3,990 Level of the Empire State Mine in Balmat, St. Lawrence County, New York. The specimen features gem-quality yellow sphalerite crystals that exhibit orange fluorescence under longwave UV light. Notably, most of the gem-quality yellow sphalerite from this mine does not fluoresce. This particular specimen is reported to originate from a single boulder mined in 2023, which was unusually encased in halite.
The sphalerite in these specimens fluoresces exclusively under longwave UV illumination, while the calcite shows fluorescence across all wavelengths, with peak brightness observed in midwave UV light. The shortwave emission spectrum of the calcite reveals a prominent peak at 340 nm in the ultraviolet range, indicating the presence of a cerium activator. Additionally, smaller peaks are detected in the longwave, midwave, and shortwave emission spectra around 477 nm and 574 nm. According to fluomin.org, these peaks may be attributed to dysprosium (Dy3+). The broad peak around 620 nm in the midwave emission spectrum is activated by manganese. The fluorescence of the sphalerite is also activated by manganese, with maximum fluorescence occurring at 570 nm in the longwave emission spectrum.
Summary of luminescence responses:
Sphalerite
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Longwave (365nm LED) UV light: Red
- Fluorescence under Midwave (305nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Red