Cuspidine from Franklin, New Jersey

Contributed by: Michael Crawford
Date: Dec 4th, 2025
Locality: Franklin Mine, Franklin, Sussex County, New Jersey, USA (See on Mindat)
Size: 12 x 16 cm

Description:
A large specimen of the rare mineral cuspidine (Ca₈(Si₂O₇) ₂F₄) with calcite from the Franklin Mine, New Jersey. In addition to the cuspidine and calcite in this specimen, there is black franklinite (Zn²⁺Fe³⁺>₂O>₄) and brown andradite (Ca₃Fe³⁺₂(SiO₄)₃) that are non-fluorescent, and there are also traces of willemite that fluoresce green.

The cuspidine and calcite in this specimen fluoresce in the ultraviolet as well as the visible region. Shortwave UV illumination of cuspidine causes an emission peak in the ultraviolet region at 342 nm and another peak at 572 nm that corresponds to its mustard yellow color. The ultraviolet emission peak shifts to 396 nm with a shoulder that extends into the violet region of visible light when cuspidine is illuminated by midwave UV light. The peak at 572 nm is still present under midwave UV illumination, but the ultraviolet-violet fluorescence is much brighter, so the midwave fluorescence has a lavender color. The ultraviolet fluorescence is caused by a lead activator, and the mustard yellow fluorescence is caused by a manganese activator. The longwave fluorescence of cuspidine has yellow-orange fluorescence with a peak at 572 nm like shortwave and midwave fluorescence. The longwave peak is a bit asymmetric compared to the shortwave and midwave peaks. There may be another activator that causes a superimposed peak at a longer wavelength.

The calcite in this specimen also has a peak in the ultraviolet at 309 nm as well as the peak at 618 nm that represents the red fluorescence. Like the cuspidine, the peak at 309 nm is activated by lead and the 618 nm peak is activated by manganese.

An image of the ultraviolet fluorescence is composed of three narrow band images taken at 310 nm, 350 nm and 394 nm. These bandpass filters are shown the plot of the emission spectra. The false color image is created by assigning the 310 nm image to blue, the 350 nm image to green and the 394 nm image to red. Cuspidine is yellow green (350 nm + 394 nm) in this image and calcite is light blue (310 nm + 350 nm).

Fluorescence under shortwave UV light.

Fluorescence under midwave UV light.

Fluorescence under longwave UV light.

Normal light.

Ultraviolet fluorescence under shortwave UV light. False color of 310 nm, 350 nm, and 394 nm bandpass images.

Emission Spectra

Summary of luminescence responses:

Cuspidine (Mindat) (RRUFF)

• Fluorescence under Shortwave (255nm LED) UV light: Yellow
• Fluorescence under Midwave (305nm LED) UV light: Violet
• Fluorescence under Longwave (365nm LED) UV light: Yellow

• Fluorescence under Longwave (365nm LED) UV light: Blue

• Fluorescence under Shortwave (255nm LED) UV light: Red