Miguelromeroite

Miguelromeroite is a member of the hureaulite group, and is the magnesium analogue of the mineral sainfeldite. It is known as a synthetic compound,[3] and was originally labeled as villyaellenite due to the very rare complex arsenate microcrystals.[2] It shows pleochroic attributes, which is an optical phenomenon that makes gems to be seen a different color depending on the axis it is being inspected. Viewing it from the Z axis, the mineral can be seen in a pale pink color. It was redefined as an intermediate species of the series. It is the full magnesium endmember of the series. Crystals are up to 4 cms in length, and are elongated on [001] with forms {100}, {110} and {101̅}.[4]

The mineral's structure is defined by an octahedral edge-sharing pentamer. The pentamers are linked into a loose framework by sharing corners with octahedra in adjacent pentamers and they are further linked through AsO₄ and AsO₃OH tetrahedra. There are three distinct octahedral sites: M1, M2, and M3. In miguelromeroite's structure, all of the octahedral sites are occupied by magnesium and the average bond lengths for the sites fall within a relatively narrow range. Though the differences in the sites suggest that the sites M2 and M3 contain small amounts of zinc and calcium.[4]

The samples were from the Veta Negra mine in Chile. Other mines include Gozaisho mine in Honshu island, Japan, and Mina Ojuela in Mapimi, Durango, Mexico. It's a type locality only in these three mines.[3]