PLATTNERITE
Plattnerite – PbO2 – is an extremely rare oxide, typically a secondary Pb mineral. It is part of oxidized Pb-Zn-Cu ores, but has no economic importance.
It is classified in the Rutile Group. It is composed of β-PbO2 and is dimorphic with scrutinyite (α-PbO2), which is also extremely rare.
1. Characteristics
Crystal system: Tetragonal, ditetragonal bipyramidal.
Color: Black in various shades: ink, iron, brownish. Tarnishes to dull.
Habit: Generally botryoidal and reniform masses. Rare crystals, in tufts, prismatic to distorted tabular, up to 5 mm. Fibrous, in concentric bands.
Cleavage: No.
Tenacity: Brittle.
Twinning: On {011}.
Fracture: Sub-conchoidal, fibrous.
Mohs Hardness: 5.5
Parting: No.
Streak: Dark brown.
Lustre: Adamantine, metallic. Dull if oxidized.
Diaphaneity: Transparent.
Density (g/cm³): 9.584
2. Geology and Deposits
Plattnerite is one of the many secondary minerals that develops in the oxidation zone of base metal deposits (Pb, Zn, Cu), typically in arid climates.
It is uncommon, being one of the very rare secondary minerals or was not identified when occurring.
3. Mineral Associations
It is associated with common gangue minerals such as quartz, calcite, and fluorite.
In the specific paragenesis of oxidation zones, it can occur with remnants of galena and sphalerite.
Among the secondary minerals with which it is associated are goethite (“limonite”), and:
– other secondary Pb minerals (cerussite, wulfenite, mimetite, pyromorphite, murdochite, leadhillite),
– secondary Zn minerals (smithsonite, hydrozincite, hemimorphite, minrecordite, rosasite, adamite, auricalcite), and
– secondary Cu minerals (malachite, azurite).
4. Transmitted Light Microscopy
Literature indicates that plattnerite has refractive indices of nω: 2.350 and nε: 2.250, has very high relief, a maximum birefringence of 0.1 (corresponding to colored to pearly hues up to the 5th order, as in carbonates) and is U(+) (Ramdohr).
5. Reflected Light Microscopy
Sample preparation: Plattnerite acquires a good polish after careful grinding. Its hardness upon polishing is much greater than that of cerussite, with which it is usually associated. In general, its hardness is far superior to that of all associated minerals.
PLANE POLARIZED LIGHT – PPL
Reflection color: Grayish-white, without any associated tint.
Compared to sphalerite, the color of plattnerite is very similar, only slightly darker.
Pleochroism: Faint, but distinct at intergranular boundaries, between gray and gray with a bluish tint.
Reflectivity: 16.78 – 17.18%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: When in well-formed crystals, distinct anisotropy between blue and greenish hues.
When in very small grains, it is pseudo-isotropic.
Internal reflections: Always present, abundant, in red/brown.
May be confused with: No information available.