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Esperite under ultraviolet light
CategorySilicate mineral
Chemical formulaPbCa3Zn4(SiO4)4
Crystal habitTypically massive
Crystal systemMonoclinic - Prismatic (2/m)
CleavageDistinct on [010] and [100] - poor on [101]
FractureConchoidal, brittle
Mohs Scale hardness5 - 5.5
Refractive indexnα = 1.762 nβ = 1.770 nγ = 1.774
Optical PropertiesBiaxial (-), 2V measured: 5° to 40°
BirefringenceMax δ = 0.012
Specific gravity4.28 - 4.42
DiaphaneitySubtranslucent to opaque
Other CharacteristicsBrilliant yellow fluorescence under SW UV; kelly green cathodoluminescence.

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 magnificient 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)
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Esperite". A list of authors is available in Wikipedia.
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