Four Color Specimen from Franklin, New Jersey
Contributed by: Michael Crawford
Date: Jun 26th, 2025
Locality: Franklin, Sussex County, New Jersey, USA (See on Mindat)
Size: 10 x 13.5 cm
Description:
A four-color specimen from Franklin Mine, Sussex County, New Jersey. The first image shows the fluorescence under shortwave UV illumination (257 nm LED). Calcite is red. Esperite (PbCa2Zn3(SiO4)3) is yellow. Willemite is green. Hardystonite (Ca2Zn[Si2O7]) is blue-violet. Franklinite is non-fluorescent and is black in the shortwave image.
Shortwave emission spectra show that the calcite, esperite and hardystonite fluoresce in the ultraviolet region as well as the visible region. The ultraviolet fluorescence calcite and hardystonite are considerably brighter than the visible fluorescence. The esperite ultraviolet fluorescence is less bright than its yellow visible fluorescence. The ultraviolet fluorescence in hardystonite, esperite and calcite are activated by lead. The ultraviolet fluorescence of calcite peaks at 310 nm. The hardystonite and esperite spectra have broader peaks with maximums 348 nm and 347 nm respectively. The visible dark violet-blue hardystonite fluorescence is the longer wave shoulder of its ultraviolet fluorescence.
The visible shortwave fluorescence of calcite, esperite and willemite is activated by manganese. The willemite emission spectrum peaks at 521 nm and is caused by manganese replacing zinc. The esperite emission spectrum peaks at 543 nm and is also caused by manganese replacing zinc. Calcite has a broader emission peak that has a maximum at 614 nm and is due to manganese replacing calcium.
The second image is a false color image and shows the ultraviolet fluorescence. The narrow bandpass filters used to create this false color image are shown on the spectral plot image. The hardystonite and esperite appear white in the image. The esperite and hardystonite cannot be distinguished in the ultraviolet image like they can in the visible image (yellow vs dark violet-blue). The calcite appears blue in the ultraviolet image because of a fluorescent peak at 310 nm.
Summary of luminescence responses:
Hardystonite
- Fluorescence under Shortwave (255nm LED) UV light: Blue
- Fluorescence under Shortwave (255nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Green