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Esperite under UV light.jpg
Esperite under ultraviolet light
Category Silicate mineral
(repeating unit)
Strunz classification 9.AB.15
Crystal system Monoclinic
Prismatic class
Color White
Crystal habit Typically massive
Crystal symmetry Monoclinic
H-M symbol: (2/m)
Space group: P21/m
Cleavage Distinct on [010] and [100] - poor on [101]
Fracture Conchoidal, brittle
Mohs scale hardness 5 - 5.5
Luster Vitreous
Streak White
Diaphaneity Subtranslucent to opaque
Specific gravity 4.28 - 4.42
Optical properties Biaxial (-), 2V measured: 5° to 40°
Refractive index nα = 1.762 nβ = 1.770 nγ = 1.774
Birefringence Max δ = 0.012
Other characteristics Brilliant yellow fluorescence under SW UV; kelly green cathodoluminescence.
References [1][2][3]

Esperite is a rare complex calcium lead zinc silicate (PbCa3Zn4(SiO4)4) related to beryllonite and trimerite that used to be called calcium larsenite. It was named in honor of Esper F. Larsen Jr. (1879–1961), petrologist of Harvard University.

Esperite has a white, greasy appearance in daylight and is much prized for its brilliant yellow green fluorescence under shortwave ultraviolet light. It is found in association with calcite, franklinite, willemite, hardystonite and clinohedrite. It has also been found as prismatic crystals up to 1 mm in length at the El Dragon Mine, Potosi, Bolivia in association with allophane, chalcomenite, clinochalcomenite and barite.


  • Mineral galleries
  • Pete Dunn, Franklin and Sterling Hill, New Jersey: the world's most magnificent mineral deposits, part 3 p. 368 (1995)
  • G. Grundmann, et al.: The El Dragon Mine, Potosi Bolivia, Mineralogical Record v.21 #2 p. 142 (1990)
  • Anthony et al., Handbook of Mineralogy, Vol. 2 (silicates) part 1 p. 225 (1995)

Robbins, Manuel: Fluorescence Gems and Minerals under Ultraviolet Light Geoscience Press pp 50–51,243 (1994)