Willemite var. Troostite from the Sterling Hill Mine, New Jersey
Contributed by: Michael Crawford
Date: Jun 21st, 2025
Locality: Sterling Hill, Ogdensburg, Sussex County, New Jersey, USA (See on Mindat)
Size: 4.5 x 6 cm
Description:
Willemite (Zn2SiO4) var. troostite crystals and calcite from the Sterling Hill Mine, Ogdensburg, Sussex County, New Jersey. Troostite is a Mn-bearing variety with MnO content between 3% and 12% weight percent. The manganese substitutes for zinc in the willemite structure. The manganese gives troostite a reddish-brown daylight color. Unlike tephroite (Mn2SiO4) which is non-fluorescent, troostite still fluoresces green.
The emission spectrum shows this troostite crystal has a peak at 521 nm. Calcite shortwave emission has a broad peak with a maximum at 623 nm. There is a second small peak at 521 nm in the calcite spectrum. This peak is the same wavelength as the troostite peak. Maybe there is some disseminated willemite in the calcite. An emission spectrum of calcite shown in fluomin.org has a signature like this calcite spectrum. There is no explanation in fluomin.org for the cause of the 521 nm peak.
The longwave emission spectra are slightly different from the shortwave spectra. The willemite peak shifts from 521 nm to 523 nm. The calcite peak shifts from 623 nm to 619 nm and the small peak at 521 nm is gone. There is an increase in calcite emission from 560 nm to 420 nm. No explanation for these differences.
Summary of luminescence responses:
Willemite
- Fluorescence under Longwave (365nm LED) UV light: Green
- Fluorescence under Midwave (305nm LED) UV light: Green
- Fluorescence under Shortwave (255nm LED) UV light: Green
- Fluorescence under Longwave (365nm LED) UV light: Red
- Fluorescence under Midwave (305nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Red