Identifying Fluorescent Minerals

## What Is Mineral Fluorescence

Fluorescence occurs when certain minerals absorb ultraviolet (UV) radiation and re-emit it as visible light. The phenomenon was named after fluorite (CaF₂), one of the first minerals observed to fluoresce. Only about 15% of mineral species show fluorescence, and it varies by locality and trace element content.

## UV Light Types

| Wavelength | Name | Best For |
|------------|------|----------|
| 365 nm | Long-wave UV (LW) | Most fluorescent minerals; safer, affordable |
| 254 nm | Short-wave UV (SW) | Some minerals only fluoresce under SW; scheelite, willemite |
| 312 nm | Mid-wave UV (MW) | Specialized; rarely needed |

**Safety**: Never look directly at UV light sources. Wear UV-blocking safety glasses. Short-wave UV requires extra caution.

## Fluorescence Color Guide

### Red/Orange Fluorescence

| Mineral | Formula | UV Response | Activator | Classic Locality |
|---------|---------|------------|-----------|------------------|
| Calcite | CaCO₃ | Red-orange (SW+LW) | Mn²⁺ | Franklin, NJ |
| Ruby (corundum) | Al₂O₃+Cr | Strong red (LW) | Cr³⁺ | Myanmar, Tanzania |
| Spinel | MgAl₂O₄+Cr | Red (LW) | Cr³⁺ | Myanmar |

### Green Fluorescence

| Mineral | Formula | UV Response | Activator | Classic Locality |
|---------|---------|------------|-----------|------------------|
| Willemite | Zn₂SiO₄ | Bright green (SW) | Mn²⁺ | Franklin, NJ |
| Autunite | Ca(UO₂)₂(PO₄)₂·10H₂O | Yellow-green (LW) | UO₂²⁺ | Worldwide |
| Hyalite opal | SiO₂·nH₂O+U | Brilliant green (LW+SW) | UO₂²⁺ | Worldwide |
| Adamite | Zn₂(AsO₄)(OH) | Green (LW) | UO₂²⁺/Cu²⁺ | Mapimi, Mexico |

### Blue/Violet Fluorescence

| Mineral | Formula | UV Response | Activator | Classic Locality |
|---------|---------|------------|-----------|------------------|
| Fluorite | CaF₂ | Blue-violet (LW) | Eu²⁺, Y³⁺ | Worldwide |
| Scheelite | CaWO₄ | Blue-white (SW) | WO₄²⁻ | Worldwide |
| Sodalite (hackmanite) | Na₈(AlSiO₄)₆Cl₂ | Orange (LW) + tenebrescence | S²⁻ | Greenland, Afghanistan |

## Phosphorescence

Some minerals continue to glow after the UV source is removed (phosphorescence). Calcite from certain localities and some diamonds show this effect.

## The Franklin, New Jersey Story

Franklin and Sterling Hill mines in New Jersey are the world's most famous fluorescent mineral localities. Over 80 fluorescent species have been found here, including the spectacular red calcite + green willemite + black franklinite assemblage.

| Mineral | Fluorescence | Daylight Color |
|---------|-------------|----------------|
| Calcite | Red-orange | White |
| Willemite | Green | Gray-green |
| Esperite | Yellow | White |
| Hardystonite | Violet-blue | White |

## Building a Fluorescent Collection

- Start with a good long-wave UV lamp (365 nm)
- Add short-wave UV for scheelite and willemite
- Display in a darkened cabinet with built-in UV lighting
- Franklin, NJ specimens are affordable and spectacular