Esperite under ultraviolet light
Category Silicate mineral
Chemical formula PbCa3Zn4(SiO4)4
Color White
Crystal habit Typically massive
Crystal system Monoclinic - Prismatic (2/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 occurred on the 400 foot level, approximately 1080 feet north of the north side of the Palmer Shaft pillar and other parts of the Franklin, New Jersey ore body.It has a white, greasy appearance in daylight and is much prized for its brilliant yellow green fluorescence under shortwave ultraviolet light. Found in association with calcite, franklinite, willemite, hardystonite and clinohedrite. Also 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.

The mineral was named in honor of Esper F. Larsen Jr. (1879-1961), petrologist of Harvard University.


  1. Webmineral
  2. Mindat
  3. Handbook of Mineralogy
  • 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)


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