| Montroydite | |
|---|---|
|   | |
| General | |
| Category | Oxide mineral | 
| Formula | HgO | 
| IMA symbol | Mtyd [1] | 
| Strunz classification | 4.AC.15 | 
| Crystal system | Orthorhombic | 
| Crystal class | Dipyramidal (mmm) H-M Symbol: (2/m 2/m 2/m) | 
| Unit cell | a = 5.52 Å, b = 6.6 Å, c = 3.52 Å; Z=4 | 
| Identification | |
| Color | Deep red, brownish red to brown | 
| Crystal habit | Long prismatic, equant, rarely flattened; striated; massive to vermicular clusters | 
| Cleavage | Perfect {010} | 
| Tenacity | Sectile | 
| Mohs scale hardness | 1.5 - 2.0 | 
| Luster | Sub-adamantine, vitreous | 
| Streak | Yellow brown | 
| Diaphaneity | Transparent to translucent | 
| Specific gravity | 11.23 | 
| Optical properties | Biaxial (+) | 
| Refractive index | nα = 2.370 nβ = 2.500 nγ = 2.650 | 
| Birefringence | δ = 0.280 | 
| Pleochroism | Deep red-orange to yellowish brown (visible in thick sections) | 
| 2V angle | Large | 
| References | [2] [3] | 
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. [2]
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. [3]