Metarauchite is a member of the

autunite Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenish fluorescent phosphate mineral with a hardness of 2–. Autunite crystallizes in the orthorhombic system and often occurs as tabular squa ...

group, found at the

Jáchymov Jáchymov (; or ''Joachimsthal'') is a spa town in Karlovy Vary District in the Karlovy Vary Region of the Czech Republic. It has about 2,300 inhabitants. Jáchymov has a long mining tradition, thanks to which it used to be the second most popu ...

ore district (type locality),

Czech Republic The Czech Republic, also known as Czechia, and historically known as Bohemia, is a landlocked country in Central Europe. The country is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the south ...

and in Schneeberg, Germany. The autunite group is a group of structured uranyl phosphates and arsenates; the other members of the group are

, bassetite,

heinrichite Heinrichite is a monoclinic-prismatic containing arsenic, barium, hydrogen, oxygen, and uranium. The mineral is named after Eberhardt William Heinrich (1918–1991) who first noted it in 1958 in the U.S. State of Oregon. Description Heinrichit ...

, kahlerite, nováčekite-I, nováčekite-II, rauchite, sabugalite, saléeite,

torbernite Torbernite, also known as chalcolite, is a relatively common mineral with the chemical formula Cu UO2)(PO4)sub>2(H2O)12. It is a radioactive, hydrated green copper uranyl phosphate, found in granites and other uranium-bearing deposits as a s ...

, uranocircite, uranospinite, and zeunerite. The mineral is named after Czech mineral collector Luděk Rauch, who died in the Jáchymov mines during mineral prospecting.

Occurrence

Metarauchite occurs as a secondary mineral in strongly oxidized polymetallic vein material. Metarauchite is found primarily in two localities, the northern part of the Jáchymov ore district, northwestern Bohemia, Czech Republic and the Heber mine, Neustädtel, Germany. It is commonly associated with metazeunerite,

erythrite Erythrite, also known as red cobalt, previously '' cobalt ochre'Krivovichev V. G.'' Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0 is a ...

, and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

(Jáchymov) and Ni-bearing metanováčekite, metazeunerite,

pharmacosiderite Pharmacosiderite is a hydrated basic ferric arsenate, with the chemical formula K Fe4( As O4)3(O H)4·(6-7) H2O and a molecular weight of 873.38 g/mol. It consists of the elements arsenic, iron, hydrogen, potassium, sodium and oxygen. It has a ...

(Schneeberg). Both localities have a surface containing strongly altered aggregates of primary ore with relics 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 ...

arsenopyrite Arsenopyrite ( IMA symbol: Apy) is an iron arsenic sulfide (FeAsS). It is a hard ( Mohs 5.5–6) metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases el ...

and nickelskutterudite and traces of native

bismuth Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs nat ...

at the Schweitzer vein in the Eduard mine.

Physical properties

Metarauchite exhibits yellow to light greenish-yellow crystals, up to 0.8 mm in size, these crystals are transparent to translucent and display vitreous to pearly luster. It exhibits a hardness of 2 on the Moh's Hardness Scale. Displays thick tabular crystals, with a prevalent pinacoid (011). Metarauchite is very brittle and shows perfect cleavage along the plane. Metarauchite does not exhibit

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

either in short- and long-wavelength ultraviolet radiation. The density of metarauchite is not easily measured because of the relatively small size of most of its crystals; hence only the calculated density from the unit cell parameters and empirical formula was obtained, giving the value 3.81 g/cm³ .

Optical properties

Metarachite is biaxial negative, it exhibits its 2V is calculated at 52°. Metarauchite is non-

pleochroic Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Etymology The roots of the word are from Greek (). It was first made compound in the German term ...

and displays no observable dispersion and a Gladstone-Dale indexhttp://webmineral.com/help/Gladstone-Dale.shtml#.WhxxFUqnEuU of 0.03.

Chemical properties

Metarauchite is a Ni- and As-dominant member of the group of hydrated uranyl arsenates and phosphates with the autunite-type sheet containing divalent cations in their inter-layer. It is only

isostructural Isostructural chemical compounds have similar chemical structures. " Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous ...

with synthetic metakirchheimerite. Metarauchite displays prominent substitution for Mg with Co, but magnesium is more commonly substituted with Ni in species found at the Schneeberg locality. The empirical formula for metarauchite is (Ni0_0.82Co_0.12Mg_0.02)_Σ0.96(UO₂)_2.01 AsO₄)_1.88(PO₄)_0.03(SiO₄)_0.02sub>Σ1.93•8.21H₂O (on the basis of 20 O,OH atoms). Simplified, the formula is Ni(UO₂)₂(AsO₂)₂•8H₂O.

Chemical composition (Jáchymov)

Chemical composition (Schneeberg)

Crystallography

Metarauchite is in the

triclinic class=skin-invert-image, 180px, Triclinic (a ≠ b ≠ c ≠ a and α, β, γ, 90° pairwise different) In crystallography, the triclinic (or anorthic) crystal system is one of the seven crystal systems. A crystal system is described by three b ...

crystal system, with a space group of P1 and is classed as a pinacoidal. The cell parameters are a = 7.194(2) Å, b = 9.759(5) Å, c = 13.231(7) Å, α = 75.53(3)°, β = 84.01(3)°, γ = 81.59(3)°, which shows an a:b:c ratio of 0.737:1:1.356. The unit cell volume is 887.53 Å³ (Calculated from Unit Cell). Metarauchite crystals show characteristic multiply twinned along .

Powder X-ray diffraction

References

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