Scrutinyite

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Scrutinyite
General
Category Oxide mineral
Formula
(repeating unit)
PbO2
Strunz classification 04.DB.20
Crystal symmetry Orthorhombic dipyramidal
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
Color Dark reddish brown
Crystal habit Crystalline, platy
Crystal system Orthorhombic
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 [1][2][3][4]

Scrutinyite /ˈskrtɨni.t/ 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.[1][3]

Identification[edit]

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,[5] its alpha form could only be recognized in 1981 and reliably identified in 1988.[3]

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).[1][3]

Characterization[edit]

Crystal structure

The PbO2 composition of scrutinyite was deduced by energy-dispersive X-ray spectroscopy. Slight oxygen deficiency is generally attributed to the surface effects, especially in thin samples, namely oxygen in the surface layers of PbO2 is usually substituted by the hydroxyl groups.[3]

The crystal structure was deduced by XRD as orthorhombic, space group Pbcn (No. 60), Pearson symbol oP12, lattice constants a = 0.497 nm, b = 0.596 nm, c = 0.544 nm, Z = 4 (four formula units per unit cell) were in reasonable agreement with previous results obtained on synthetic samples.[3]

References[edit]

  1. ^ a b c Scrutinyite at Webmineral
  2. ^ Scrutinyite at Mindat
  3. ^ a b c d e f J. E. Taggard, Jr. et al. (1988). "Scrutinyite, natural occurrence of α-PbO2 from Bingham, New Mexico, U.S.A., and Mapimi, Mexico". Canadian Mineralogist 26: 905. 
  4. ^ Handbook of Mineralogy
  5. ^ Haidinger W (1845) Zweite Klasse: Geogenide. II. Ordnung. Baryte VII. Bleibaryt. Plattnerit., p. 500 in Handbuch der Bestimmenden Mineralogie Bei Braumüller and Seidel Wien pp. 499-506 (in German)

External links[edit]