Eveite is a manganese arsenate mineral in the olivenite group. Its chemical formula is Mn2AsO4OH. It is an orthorhombic-dipyramidal apple-green mineral containing arsenic, hydrogen, manganese, and oxygen. The name, for the biblical “Eve”, comes from its structural similarities to adamite and is also a reference to its apple-green color. It can also be pale yellow.
It is relatively low-density and is associated with high hydrate and low-density arsenates in open cavities, which contributes to its rarity.
- Category: Arsenate minerals
- Formula: Mn22+AsO4OH
- Crystal system: Orthorhombic
- Crystal class: Dipyramidal (mmm)
Eveite is an orthorhombic mineral, which means it has three crystallographic axes of unequal lengths which are at 90° to one another. It is anisotropic, which means that its physical and optical properties differ with respect to direction. It has high relief, which is the apparent topography exhibited by minerals in thin section as a consequence of refractive index. It is biaxial, so it has two optic axes and three indices of refraction n depending on the crystallographic direction. The refractive index is the ratio of the velocity of light in a vacuum to that in the mineral.
- Formula mass: 265.80 g/mol
- Color: Apple green, pale yellow
- Crystal habit: Tabular or sheaf-like
- Mohs scale hardness: 3.5 – 4
- Luster: Vitreous
- Streak: White
- Diaphaneity: Semitransparent
- Specific gravity: 3.76
- Optical properties: Biaxial
It is found only in Långban, Filipstad, Värmland, Sweden and at the Sterling Mine in New Jersey, United States. It is a dimorph of sarkinite and is isostructural with adamite.
Eveite is significant because it was the first mineral to show Mn2+ atoms in five-fold coordination, which is otherwise undocumented in mineral structures. It’s an important addition to the olivenite group, and isostructural with andalusite. Because it shows up in very small quantities and in only two locations, it has no commercial use.