Gauthierite is a very rare

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

with the idealised chemical sum formula . It is a

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

hydrated In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

orange-coloured lead potassium

uranyl The uranyl ion with the chemical formula has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen, with uranium in the oxidation state +6. Four or more ligands may be bound to the u ...

oxide

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

. It was found by analysing old mineral specimens, and is only known from one locality, the

Shinkolobwe Mine Shinkolobwe, or Kasolo, or Chinkolobew, or Shainkolobwe, was a radium and uranium mine in the Haut-Katanga Province of the Democratic Republic of the Congo (DRC), located west of Likasi (formerly Jadotville), south of Kambove, and about north ...

in the

Democratic Republic of the Congo The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...

. The mineral was named in honour of Gilbert Gauthier, a Belgian collector of

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

minerals, who provided a sample to one of the co-authors of the study that first identified it in 2017.

Etymology and history

Gauthierite is a very rare mineral and was first described in 2017. It was discovered on an old mineralogical sample from

. A co-author of the original study was given the sample by Gilbert Joseph Gauthier (24. December 1924 – 23. June 2006), a Belgian mineral collector who focused on uranium minerals, after whom the mineral was named.

Classification

According to the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. ...

(IMA), which last updated its list in 2009, the Nickel-Strunz system lists gauthierite in the section of "oxides and hydroxides" amongst the "uranyl hydroxides". There it forms the group 4.GB, together with leesite K(H₂O)₂ UO₂)₄O₂(OH)₅�3H₂O, shinkolobweite Pb_1.25 ⁵⁺(H₂O)₂(U⁶⁺O₂)₅O₈(OH)₂H₂O)₅ and kroupaite KPb_0.5 UO₂)₈O₄(OH)₁₀�10H₂O.

Chemistry

An analysis by

electron microprobe An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. I ...

using nine samples of the type material gave an averaged composition of 1.29 w.-% K₂O, 7.17 w.-% PbO, 82.10 w.-% UO₃ and 8.78 w.-% H₂O. Based on 34 oxygen atoms this gives the empirical sum formula K_0.67Pb_0.78U₇O₃₄H_23.77, which is idealised as KPb UO₂)₇O₅(OH)₇��8H₂O. left, Gauthierite single crystal (app. 0.1 mm) Gauthierite crystallises monoclinically in space group ''P''2₁/''c'' with the lattice parameters ''a'' = 29.844(2) Å; ''b'' = 14.5368(8) Å and ''c'' = 14.0406(7) Å and β = 103.708(6)° with eight formula units per

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

. The crystal structure is related to that of vandendriesscheite. Together with

fourmarierite Fourmarierite is a secondary uranium-lead mineral. It was named for the Belgian geologist Paul Fourmarier (1877–1970). Its chemical formula is . References Lead minerals Uranium(VI) minerals Orthorhombic minerals Minerals in space group ...

these three minerals form a group of early stage alteration products which are formed in the oxidation-hydration weathering of

uraninite Uraninite, also known as pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium c ...

. This is particularly prominent in the amount of water between the uranyl layers. Because of its uranium content of about 67.2% the material is strongly

Occurrence and localities

Gauthierite has so far been only identified on old mineralogical samples from its type locality

in the Democratic Republic of the Congo. The mineral is associated on the

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

with

soddyite Soddyite is a mineral of uranium. It has yellow crystals and usually mixed with curite in oxidized uranium ores. It is named after the British radiochemist and physicist Frederick Soddy (1877–1956). Soddyite has been a valid species since 192 ...

sklodowskite Sklodowskite is a uranium mineral with the chemical formula: Mg(UO2)2(HSiO4)2·5H2O. It is a secondary mineral which contains magnesium and is a bright yellow colour, its crystal habit is acicular, but can form in other shapes. It has a Mohs h ...

and a member of the metazeunerite-

metatorbernite Metatorbernite (or meta-torbernite) is a radioactive phosphate mineral, and is a dehydration pseudomorph of torbernite. Chemically, it is a copper uranyl phosphate and usually occurs in the form of green platy deposits. It can form by direct depo ...

series. The matrix of the type material is

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

with disseminated altered

. The mineral may form by weathering of uraninite in the presence of

radiogenic A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive (a radionuclide) or stable (a stable nuclide). Radiogenic nuclides (more commonly referred to as radiogenic isotopes) form some of ...

lead, while potassium may be leached from other

gangue Gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body that are di ...

materials.

References

External links

* {{Commonscat inline, Gauthierite
Gauthierite
in the ''Handbook of Mineralogy'', Mineralogical Society of America Geology of the Democratic Republic of the Congo Lead minerals Uranium(VI) minerals Oxide minerals Hydroxide minerals Potassium minerals Octahydrate minerals Radioactive minerals Monoclinic minerals Minerals described in 2017