| Esperite | |
| Category: | Silicate mineral |
| Formula: | PbCa3Zn4(SiO4)4 |
| Imasymbol: | Epr[1] |
| Strunz: | 9.AB.15 |
| System: | Monoclinic |
| Class: | Prismatic (2/m) (same H-M symbol) |
| Symmetry: | P21/m |
| Color: | White |
| Habit: | Typically massive |
| 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 |
| Streak: | White |
| Gravity: | 4.28–4.42 |
| Diaphaneity: | Subtranslucent to opaque |
| Other: | Brilliant yellow fluorescence under SW UV; kelly green cathodoluminescence. |
| References: | [2] [3] [4] |
Esperite is a rare complex calcium lead zinc silicate (PbCa3Zn4(SiO4)4) related to beryllonite and trimerite that used to be called calcium larsenite.
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)