Scrutinyite
| Scrutinyite | |
|---|---|
| General | |
| Category | Oxide mineral |
|
Formula (repeating unit) |
PbO2 |
| Strunz classification | 4.DB.20 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H–M Symbol: (2/m 2/m 2/m) |
| Space group | Pbcn |
| Unit cell | a = 4.91 Å, b = 5.95 Å c = 5.43 Å; Z = 4 |
| Identification | |
| Formula mass | 239.20 g/mol |
| Color | Dark reddish brown |
| Crystal habit | Crystalline, platy |
| Cleavage | {100} perfect, {010} imperfect |
| Fracture | Brittle |
| Luster | Sub-metallic |
| Streak | Dark brown |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 9.867 (calculated) |
| Optical properties | Biaxial |
| Refractive index | n > 2 |
| Other characteristics | Non-fluorescent, nonmagnetic |
| References | |
Scrutinyite /ˈskruːtᵻni.aɪt/ is a rare oxide mineral and is the alpha crystalline form of lead dioxide (α-PbO2), plattnerite being the other, beta form. The mineral was first reported in 1988 and its name reflects the scrutiny and efforts required to identify it from a very limited amount of available sample material.
The synthetic orthorhombic form of lead dioxide, α-PbO2, was known from 1941. Although natural lead dioxide has been known, as the mineral plattnerite (β-PbO2), since 1845, its alpha form could only be recognized in 1981 and reliably identified in 1988.
The new mineral was spotted in several samples collected at Bingham, New Mexico and Mapimí, Durango, Mexico. It was first thought to be minium (lead tetroxide mineral) because of its high lead content, brown color and association with other lead oxide minerals plattnerite and murdochite. Its holotype specimen consisted of crystalline plates 25–30 micrometers (µm) across and 1–2 µm thick with the total weight below 1 mg. The flakes were collected from a fluorite, quartz, limonite and rosasite matrixes. Identification and characterization of scrutinyite by the standard X-ray diffraction (XRD) technique was hindered by scarcity of material and strong signal interference with plattnerite. The unusual amount of effort required for the analysis resulted in its name derived from the word "scrutiny". The holotype specimen is preserved in the US National Museum (catalog number NMNH 165479).
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