Hydroxyplumbopyrochlore

Chemical formula: (Pb<sup>2+</sup><sub>1.5</sub>&#9744;<sub>0.5</sub>)Nb<sup>5+</sup><sub>2</sub>O<sub>6</sub>(OH)

A rare mineral from the pyrochlore group, a hydrated lead niobate, forming characteristic, octahedral crystals with a resinous luster.

## Characteristics Hydroxyplumbopyrochlore is a rare mineral belonging to the pyrochlore group. It is a hydrated lead niobate, and its name refers to its chemical composition (hydroxyl, lead) and structural similarity to pyrochlore. It usually occurs in the form of well-formed, octahedral crystals, which may be modified by other forms. Crystals rarely exceed a few millimeters in size. Its surface is often dull or covered with a coating. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of about 4. It is heavy and brittle, with a density reaching up to 6.35 g/cm³. The luster is most often resinous to metallic on fresh fracture surfaces, but can be dull on external surfaces. It is opaque, only translucent on thin edges. ## Colors and Varieties Hydroxyplumbopyrochlore ranges in color from yellow, through orange, reddish-brown, brown, to black. No commercial or color varieties are distinguished. ## History and Name The mineral was first described in 1977 by D.D. Hogarth, G.Y. Chao, and A.G. Plant based on material from the St-Amable mine in Quebec, Canada. Its name comes from the dominant components: the hydroxyl group (OH), lead (Latin: *plumbum*), and its relation to the structure of the pyrochlore group. It was disqualified as a distinct mineral species in 2010 as part of the redefinition of the pyrochlore supergroup and is currently classified as a hydroxyl-rich variety of plumbopyrochlore. ## Uses Due to its rarity and small crystal size, hydroxyplumbopyrochlore has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals from the pyrochlore group.

Properties

Mohs hardness
4
Luster
Resinous to metallic
Streak
Light brown
Density
6.3 - 6.35
Cleavage
Indistinct on {111}
Fracture
Conchoidal to uneven
Transparency
Translucent to opaque
Crystal system
Cubic

Diagnostic features

## Identification A key diagnostic feature is the crystal habit – they are almost always regular octahedra. Also characteristic are the resinous to metallic luster, high density (the specimen is heavy for its size), and occurrence in specific geological environments (carbonatites, nepheline syenites). ## Distinguishing from Similar Minerals It can be confused with other minerals from the pyrochlore group (e.g., plumbopyrochlore, pyrochlore), from which differentiation without advanced chemical analysis (EDS/WDS) is practically impossible. From other minerals with a similar appearance, such as magnetite or some garnets, it is distinguished by lower hardness, lack of magnetism, and a specific, resinous luster. ## Crystal Forms Most often, it forms single, well-formed octahedral crystals {111}, less frequently in combination with a cube {100}. Crystals are usually small, ranging from sub-millimeter to several millimeters in size.

Geological environment

## Genesis Hydroxyplumbopyrochlore is a mineral of magmatic origin, crystallizing in the late stages of alkaline rock formation, such as carbonatites and nepheline syenites. It forms under conditions of low temperature and elevated activity of volatile components. ## Mineral Associations It often co-occurs with minerals such as aegirine, microcline, nepheline, calcite, biotite, zircon, apatite, and other minerals from the pyrochlore group. ## Localities The most important and well-documented localities worldwide include the type locality at Mont St-Amable in Quebec (Canada) and the Khibiny Massif on the Kola Peninsula in Russia. It has also been reported in the Ilímaussaq complex in Greenland.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with sharp, well-formed, and undamaged octahedral crystals, clearly set on a contrasting rock matrix (e.g., on white calcite or aegirine), are most valued by collectors. An intense, resinous luster and an attractive, orange or reddish-brown color are also desirable. Crystal size is a key factor influencing value. ## Popular Localities Specimens from the Canadian type locality (Mont St-Amable) and the Russian Kola Peninsula are the most classic and sought-after examples of this mineral in collections.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to the lead content and possible reactivity, contact with water and any chemical agents should be avoided. It is recommended to wash hands after handling the mineral. ## What to Avoid Contact with acids and other chemicals that could damage the mineral must be absolutely avoided. It is brittle and sensitive to impact. It should not be heated or subjected to ultrasound. ## Storage It is recommended to store it in stable conditions, in a closed display box, to protect it from dust, mechanical damage, and moisture. It should be kept away from other minerals that it could scratch or that could damage it.

Sources

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