Miguelromeroite
General
Category	Mineral
Formula (repeating unit)	MnS(AsO4)2(HAsO4)2 · 4H2O
IMA symbol	Mig[1]
Crystal system	Monoclinic
Crystal class	Prismatic H-M symbol: 2/m
Space group	B2/b
Unit cell	1,624.38
Identification
Color	Salmon pink to orange
Twinning	None observed
Cleavage	Good on {100}
Fracture	Conchoidal
Mohs scale hardness	4
Luster	Vitreous
Streak	Pale pink
Diaphaneity	Transparent
Density	3.69
Optical properties	Biaxial (−)
Refractive index	nα = 1.713 nβ = 1.723 nγ = 1.729
Birefringence	0.016
Pleochroism	Visible
2V angle	Measured: 70° Calculated: 75°

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.

Properties

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]

Structure

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]

Mines

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]

References