Rameauite
General
Category	Oxide mineral
Formula (repeating unit)	K2Ca(UO2)6OH16·H2O or K2CaU6+6O20·9H2O
IMA symbol	Rme[1]
Strunz classification	4.GB.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a= 13.97 Å, b= 14.26 Å c= 14.22 Å, β = 121.02°: Z = 4
Identification
Formula mass	2,028.57 g/mol
Color	Orange
Crystal habit	Prismatic and/or can consist of a hexagonal outline
Twinning	On {100}
Cleavage	Good cleavage
Diaphaneity	Semitransparent
Density	5.6
Optical properties	Biaxial Negative
Refractive index	a= n.d. β= 1.95 γ= 1.97
2V angle	32° (meas.)
Other characteristics	Radioactive
References	[2][3][4]

Rameauite is a hydrated complex uranyl oxide mineral with formula K₂Ca(UO₂)₆OH₁₆·H₂O^[5] or K₂CaU⁶⁺₆O₂₀·9H₂O.^[4]

Crystallography

Rameauite has four observed forms which are {010}, {100}, {001} and {110}. The angles between these faces are {100}^{001} = 58°40' and {010}^{110} = 49° 50'. The crystals are always twinned on {100} and they are flattened parallel to {010}, and elongated parallel to {001}. The mineral rameauite is an example of a monoclinic mineral and appears pseudo-hexagonal. I has unit cell dimensions of: a= 13.97, b= 14.26, c= 14.22 with β = 121.02°.^[4][6]

Occurrence

It was first described in 1972 for an occurrence in the Margnac Mine, Compreignac, Haute-Vienne, Limousin, France and named after Jacques Rameau (1926–1960), French prospector at the "Commissariat à l'Energie Atomique", who discovered the deposit where the mineral occurs.^[4][5] In addition to the type locality in France it has been reported from the Orphan Mine on the south rim of the Grand Canyon in Arizona and on Rhyolite Ridge, Esmeralda County, Nevada.^[5]

References