Willemite, zinc silicate,
Crystal system: Trigonal.
Density: 4.0 gms/cm3
Colour: White, yellow, green or brown.
Streak: Not given.
Fluorescent willemite from Franklin, New Jersey occurs in combination with a large number of other minerals, both fluorescent and non-fluorescent. One attractive combination is green fluorescing willemite with red fluorescing calcite. Willemite from Franklin also exhibits long phosphorescence up to 10 seconds. The activator is thought to be arsenic.
This specimen of willemite with calcite in the picture is from Franklin, New Jersey, and is shown fluorescing under short wave ultraviolet radiation.