Vladimirite

In terms of its optical properties, vladimirite is anisotropic which means the velocity of light varies depending on direction through the mineral.

It is colorless in plane polarized light, and it is weakly pleochroic.

Pleochroism is the variety of colors under plane polarized light displayed by crystals at various angles.

[4] It is a secondary mineral in the oxidized zone of arsenic-bearing ore deposits.

It has been reported from the Richelsdorf Mountains, Hesse, Germany; the Bou Azzer district, Morocco and the Mohawk mine, Keweenaw County, Michigan.