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 light.

It is found in association with calcite, franklinite, willemite, hardystonite and clinohedrite.

It has also been 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.

Robbins, Manuel: Fluorescence Gems and Minerals under Ultraviolet Light Geoscience Press pp 50–51,243 (1994)