Cervandonite

[4] It was first described by Buhler Armbruster in 1988, but it has proven to be problem due to the extreme scarcity of single crystals and its unusual replacement of silicon and arsenic.

[6] The exact fragment was re-examined with MoKα radiation using BRUKER Apex II diffractometer equipped with a 2K CCD detector.

Through the use of X-ray diffraction, the unusual nature of the As to Si substitution found arsenic to be present as As3+ instead of As5+, with the presence of sorosilicate Si2076− anions were also established.

After accurate determination of the crystal structure the As and Si atoms where shown to occupy distinct cell sites.

The mineral is brittle, porous, rosettelike aggregate, with adamantine luster, poorest at {001} cleavage, conchoidal fracture with a brownish-black streak,[9] and a hardness= 5.0.