Willemite is a zinc nesosilicate famous as the brilliantly fluorescent green mineral of the Franklin and Sterling Hill Zn-Mn deposits in New Jersey. Under shortwave UV, willemite emits an intense yellow-green glow that defined the entire genre of mineral fluorescence display.
Properties
- Formula: Zn2SiO4
- Crystal system: Trigonal
- Hardness: 5.5
- Color: Yellow-green, brown, white, gray; gem grade rare
- Streak: White
- Luster: Vitreous to resinous
- Cleavage: Indistinct on {0001}
- Density: 3.9 – 4.2 g/cm³
Occurrence
Type locality: Vieille Montagne (Belgium). World’s premier source: Franklin and Sterling Hill (New Jersey, USA), where willemite is a primary ore associated with franklinite, zincite and calcite. Also at Tsumeb (Namibia), where gem-quality green crystals occur.
Identification
SW UV fluorescence is essentially diagnostic — green-yellow glow under 254 nm UV. Color in daylight ranges from pale green to dark brown. Hexagonal/trigonal prismatic crystals when well-formed.
Collector Notes
Franklin display rocks combining willemite (green fluorescence) with calcite (red fluorescence) are iconic and remain a flagship of any UV-mineral collection. Pair with hardystonite for the complete Franklin fluorescent-silicate suite.
Found at these Localities
- Broken Hill (布罗肯希尔铅锌银矿)
- Franklin and Sterling Hill (富兰克林矿(新泽西))
- Tsumeb Mine (楚梅布矿)
