Esperite

Infobox mineral
name = Esperite
category = Silicate mineral
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caption = Esperite under ultraviolet light
formula = PbCa₃Zn₄(SiO₄)₄
color = White
habit = Typically massive
system = Monoclinic - Prismatic (2/m)
twinning =
cleavage = Distinct on [010] and [100] - poor on [101]
fracture = Conchoidal, brittle
mohs = 5 - 5.5
luster = Vitreous
refractive = nα = 1.762 nβ = 1.770 nγ = 1.774
opticalprop = Biaxial (-), 2V measured: 5° to 40°
birefringence = Max δ = 0.012
pleochroism =
streak = White
gravity = 4.28 - 4.42
melt =
fusibility =
diagnostic =
solubility =
diaphaneity = Subtranslucent to opaque
other = Brilliant yellow fluorescence under SW UV; kelly green cathodoluminescence.
references = [http://webmineral.com/data/Esperite.shtml Webmineral] [http://www.mindat.org/min-1412.html Mindat] [http://www.minsocam.org/msa/Handbook/Esperite.PDF Handbook of Mineralogy]

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.

References

* [http://mineral.galleries.com/minerals/silicate/esperite/esperite.htm 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)