Esperite
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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 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, 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.
Properties: Crystal data: Monoclinic typically as granular aggregates (note exception at El Dragon Mine) Optical properties: Translucent, color white luster slightly greasy Physical properties: Hardness 5 to 5.5, density 4.28 to 4.42 brilliant greenish yellow fluorescence under short wave ultraviolet (presumed activator divalent manganese)
The mineral was named in honor of Esper F. Larsen Jr.
[edit] References
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)
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