Esperite is a rare complex calcium lead silicate 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.[clarification needed
Esperite has a white, greasy appearance in daylight and is much prized for its brilliant yellow green fluorescence under shortwave ultraviolet, franklinite , hardystonite. It has also been found as prismatic crystals up to 1 mm in length at the El Dragon Mine in association with allophane , clinochalcomenite.