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| Imasymbol: | Mig[1] |
| System: | Monoclinic |
| Class: | Prismatic H-M symbol: 2/m |
| Symmetry: | B2/b |
| Unit Cell: | 1,624.38 |
| Color: | Salmon pink to orange |
| Twinning: | None observed |
| Cleavage: | Good on |
| Fracture: | Conchoidal |
| Mohs: | 4 |
| Luster: | Vitreous |
| Opticalprop: | Biaxial (−) |
| Refractive: | nα = 1.713 nβ = 1.723 nγ = 1.729 |
| Birefringence: | 0.016 |
| Pleochroism: | Visible |
| 2V: | Measured: 70° Calculated: 75° |
| Streak: | Pale pink |
| Density: | 3.69 |
| Diaphaneity: | Transparent |
Miguelromeroite is a mineral named for Miguel Romero Sanchez by Anthony Robert Kampf. The mineral, first described in 2008[2] was named in 2009, the same year it got approved by the International Mineralogical Association.
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. 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, and .
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.