QUENSELITE
Quenselite – PbMnO2(OH) – is an extremely rare hydroxide. It is not an ore, despite containing 66.59% Pb and 17.66% Mn by weight.
It is probably more common than the few existing records suggest; it just wasn’t recognized because Mn ores, in general, are made up of minerals typically occurring in extremely small, submicroscopic crystals. In these ores, investigations are generally limited to determining the Mn oxide content, without devoting special interest to mineralogy.
1. Characteristics
Crystal system: Monoclinic prismatic.
Color: Black. Its sharp edges are transparent with dark brown color.
Habit: Tabular crystals can be somewhat elongated and may show rounded vertices.
Cleavage: {001} perfect, almost like mica. Striations in {011},
// at {100}.
Tenacity: Flexible, something malleable
Twinning: Contact and lamellar, common.
Fracture: No information available.
Mohs Hardness: 2.5
Parting: No.
Streak: Dark brownish gray.
Lustre: Adamantine metallic
Diaphaneity: Transparent.
Density (g/cm³): 6.84
2. Geology and Deposits
Quenselite, according to the literature, occurs in metamorphic manganese deposits. However, records of quenselite occurrences are either from various types of deposits or are not precise enough to describe the specific deposit type:
– Mudgee (Australia) refers to a large region with coal and iron mines (based on magnetite).
– Shengli Pipes (China) is an occurrence of kimberlite pipes.
– Shivrajpur (India) is an occurrence of Mn ore.
– Mori Mine (Japan) is a Miocene hydrothermal vein in granodiorite.
– Belyaevsky Rise (Sea of Japan, Pacific Ocean) is a submarine mountain with ferromagnesian crusts and basalts containing Cu, Zn, Sn, Ni, Pb, As, Ag, La, Ce, Nd, and Pr.
– America Stope (Langban, Sweden) is one of the hematite and magnetite-based Fe mines in the Bergslagen Mining District.
– Lucy Bay (Scotland, UK) is apparently an occurrence of Mn minerals.
– Burgin Mine (Utah, USA) is a Pb mine with 47 different minerals recorded.
3. Mineral Associations
It is associated with barite, calcite and a series of Mn minerals: braunite, hausmannite, bixbyite, jacobsite, psilomelane.
4. Transmitted Light Microscopy
In PPL, quenselite has a refractive index of 2,300, a deep brown color, and moderate relief.
In XPL, its maximum birefringence is 2.3.
In Convergent Light, it is B(+).
5. Reflected Light Microscopy
Sample preparation: Like other Mn hydroxides, quenselite has a low polishing hardness, but it polishes well easily. Impregnation is probably necessary to properly polish the small crystals.
PLANE POLARIZED LIGHT – PPL
Reflection color: Bluish gray. When viewed at lower magnifications, the color is creamy gray.
Pleochroism: No.
Reflectivity: 19.87 – 22.02% In the specific paragenesis, quenselite is generally the lightest mineral, much lighter than braunite and hausmannite.
Bireflectance: Very faint, more noticeable along twinning shots.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Distinct to strong anisotropy along twin planes and in sections parallel to (100), at NC+2º: light gray or light bluish to dark gray-brown. With well-crossed nicols, random sections show very weak anisotropy.
Internal reflections: Usually present, with colors ranging from deep red to yellowish-brown. They can be abundant, but only in observations in immersion oil.
May be confused with: other Mn minerals, because the presence of quenselite is not expected and the mineral is confused with other more abundant Mn minerals.
General Characteristics:
Grain shape: Generally occurs in very small crystals (<1mm) in open fissures in Mn ores.
Well-developed cleavage is typical.
Twinning is very common, usually simple twinning, which may show irregular boundaries. Twinning similar to that of plagioclase, with lamellae of different widths, may occur. There are also aggregates of twinning with three individuals (“trillings”).
Substitutions: quenselite substitutes pyrolusite and cryptomelane.
Corrosion is observed in the crystals, with corrosion starting internally along the cleavage planes.