Montroydite

Montroydite is the mineral form of mercury(II) oxide with formula HgO. It is a rare mercury mineral. It was first described for an occurrence in the mercury deposit at Terlingua, Texas and named for Montroyd Sharp who was an owner of the deposit.

Montroydite
Vein of dark red montroydite and orange kleinite in a matrix of white calcite
General
CategoryOxide mineral
Formula
(repeating unit)
HgO
IMA symbolMtyd
Strunz classification4.AC.15
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M Symbol: (2/m 2/m 2/m)
Unit cella = 5.52 Å, b = 6.6 Å, c = 3.52 Å; Z=4
Identification
ColorDeep red, brownish red to brown
Crystal habitLong prismatic, equant, rarely flattened; striated; massive to vermicular clusters
CleavagePerfect {010}
TenacitySectile
Mohs scale hardness1.5 - 2.0
LusterSub-adamantine, vitreous
StreakYellow brown
DiaphaneityTransparent to translucent
Specific gravity11.23
Optical propertiesBiaxial (+)
Refractive indexnα = 2.370 nβ = 2.500 nγ = 2.650
Birefringenceδ = 0.280
PleochroismDeep red-orange to yellowish brown (visible in thick sections)
2V angleLarge
References

Montroydite occurs in mercury deposits of hydrothermal origin. Associated minerals include: native mercury, cinnabar, metacinnabar, calomel, eglestonite, terlinguaite, mosesite, kleinite, edgarbaileyite, gypsum, calcite and dolomite.

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