Eur. J. Mineral.
2000, 12, 1045-1050

Rollandite, Cu3 (AsO4)2 . 4H2O, a new mineral:its description and crystal structure
HALIL SARP1* and RADOVAN ČERNÝ2
1Département de Minéralogie du Muséum d’histoire naturelle de la Ville de Genève,

1 route de Malagnou, CP 6434, CH-1211 Genève 6, Suisse
2Laboratoire de Cristallographie, Université de Genève,

24 quai Ernest-Ansermet, CH-1211 Genève 4, Suisse

Abstract: Rollandite, Cu3 (AsO4)2 .4H2O, was found in the old copper mines of Roua (Alpes-Maritimes, France),
associated with olivenite, conichalcite, clinotyrolite, cornubite, kolfanite, pharmacosiderite, gerhardtite, atacamite,gilmarite, wallkilldellite-Fe, cuprite, domeykite, algodonite and native copper. It forms aggregates (1mm diameter)
consisting of perfect crystals (0.5 x 0.15 x 0.1 mm maximum dimension). The bottle-green crystals are elongatedalong a, slightly flattened on {010}, and have a good cleavage on {001}. They are not twinned. The mineral isorthorhombic, Pnma, a = 5.6906(4), b = 17.061(1), c = 9.732(1) Å, V = 944.9(1) Å3, Z = 4, Dmeas = 3.9(1) and Dcalc= 3.84 g/cm3. The strongest lines in the X-ray powder diffraction pattern (dobs in Å, (hkl), Ivis) are: 8.52, (020), 100;
3.721, (131), 60; 3.221, (141) (051), 90; 3.102, (132), 40; 2.817, (103)(033), 35; 2.795, (142), 35; 2.350, (143) (053),
25; 2.133, (080) (251), 25. Mohs’ hardness is 4-4.5. Luster is vitreous transparent, streak is very light green; crystals
are biaxial (-) with α = 1.745(5), β = 1.755(5), γ = 1.760(5) at 590 nm; 2Vobs = 71(2)°, 2Vcalc = 70.1(4)°. Nonpleochroic. The crystal structure was solved by direct methods (MoKα radiation) and refined using 1407 observed
unique reflections to R = 0.086, Rw = 0.046. The structure of rollandite is formed by (020) sheets of Cu1O6 octahedra and [100] chains of Cu2O5 square pyramids linked by AsO4 tetrahedra. The water molecule O6H2 is bonded byhydrogen bonds in the channels running along [100].
Key-words: rollandite, new mineral, powder pattern, crystal structure, arsenate, copper, hydrogen bonding.

Introduction
Rollandite, Cu3 (AsO4)2.4H2O, is a new mineral discovered in samples collected by DanielleMari, Gilbert Mari and Pierre Rolland in the oldcopper mines of Roua, which are situated in thenorthwestern part of the Alpes-Maritimes department (France).
The mineral name honours Pierre Rolland(1940 -), an eminent mineral collector of the Roua
mines who works in the well-known Oceanographic Museum of the principality of Monaco.

The mineral and mineral name have been
approved by the Commission on New Minerals
and Mineral Names of the International
Mineralogical Association.
Type material is preserved in the Departmentof Mineralogy of the Natural History Museum ofGeneva, Switzerland, under reference no. 447.008

Occurrence
The new mineral described occurs in the Roua*e-mail: halil.sarp@mhn.ville-ge.ch

DOI: 10.1127/0935-1221/2000/0012-1045 $ 1.50
 2000 E. Schweizerbart’sche Verlagsbuchhandlung. D-70176 Stuttgart

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H. Sarp, R. Černýcopper occurrences (South group) in the upper
part of the Var valley (the Daluis gorge) at thewestern margin of the Barrot Dome. The metallogeny and geology of this Dome have been studied by Vinchon (1984) and Mari (1992). In theRoua ore deposit, the cupriferous mineralisation ishosted in a gangue formed by dolomite, calcite
and aragonite, and consists of native copper,
cuprite, domeykite, algodonite, koutekite andnative silver. Detailed mineralogical study of thisore deposit produced several secondary, rare andunknown mineral species (Sarp et al., 1994, 1995,1996). The new mineral described here occurs insmall geodes in association with olivenite,
conichalcite, clinotyrolite, cornubite, kolfanite,
pharmacosiderite, gerhardtite, atacamite, gilmarite(Sarp & Černý, 1999), wallkilldellite-Fe (Sarp etal., 1999), cuprite, domeykite, algodonite andnative copper.

Physical and optical properties
Rollandite occurs as aggregates of maximum
size 1mm in diameter, which are formed by perfect
crystals of maximum size 0.5 x 0.15 x 0.1 mm.
The crystals are elongated parallel to a, slightlyflattened on {010} and have one good {001}cleavage; they are not twinned. The most developed forms are {010}, {011}, {101} and {001}(Fig. 1). The crystals are bottle-green, transparent,with vitreous lustre and very light green streak.

Fig. 1. SEM image of rollandite crystals, elongated parallel to a, and slightly flattened on {010}. Acicular crystals are olivenite.

The mineral is very brittle with conchoidal fracture. The Mohs’ hardness is 4-4.5. The density,
measured by flotation in heavy liquid, is 3.9 (1)g/cm3 and the calculated density is 3.84(1) (basedon the empirical formula) and 3.80 g/cm3 (basedon the ideal formula). The mineral is soluble in
HCl. It is nonfluorescent and nonpleochroic.
Rollandite is biaxial negative, with α = 1.745(5),β = 1.755(5), γ = 1.760(5) (determined at 590 nm),2Vobs = 71(2)° and 2Vcalc = 70.1(4)°. The dispersion (r < v) is strong. The optical orientation is:O.A.P.//{001}, α = a, β = c, γ = b.

Chemical composition
Rollandite was analyzed with a Cameca electron microprobe, using operating voltage of 15kV, beam current of 15 nA, and a beam size of 10µm. Qualitative examination showed only Cu andAs. For quantitative analysis, trippkeite (Cu, As),
copper metal (Cu) and arsenic metal (As) wereused as standards. The results are given in Table 1.
Table 1. Chemical analysis [wt.%] of rollandite.

The H2O was estimated by difference due toinsufficient sample. The empirical formula basedon 12 oxygen atoms is: Cu3.09As2.02H7.71O12 andthe idealized formula, Cu3(AsO4)2.4H2O, wasconfirmed by structure determination. The
Gladstone-Dale constants of Mandarino (1981)
along with the oxide proportions, determinedfrom the electron-microprobe data and from thecrystal structure, lead to Kc values of 0.188 and0.189 respectively. The value of Kp, calculatedusing the average index of refraction (1.753), andthe calculated density from the empirical formula,is 0.196. For the same average index of refraction
and the calculated density from the idealized formula, Kp is 0.198. The compatibility index is 0.043 for the empirical formula, and -0.048 forthe idealized formula, indicating good compatibility (Mandarino, 1981) between the physicaland chemical data.

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X-ray crystallography
Powder-diffraction data (Table 2) wereobtained using a Gandolfi camera (114.6 mm1047

diameter, Ni-filtered CuKα radiation). The relative
intensities of the reflections were estimated visually. A single-crystal of rollandite 0.128 x 0.032 x0.016 mm in size was examined by the precession

Table 2. X-ray powder diffraction data for rollandite (d in Å).

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H. Sarp, R. Černýmethod (Ni-filtered CuKα) and the same crystal
was measured on an Enraf-Nonius CAD4 diffractometer with monochromatized MoKα radiationin θ/2θ scanning-mode with limits -7 < h < 7, -23< k < 23, -13 < l < 13. A total of 3246 reflections
was measured up to θ = 30°. Lattice parameters
were refined on the basis of 25 reflections with8.5° < θ < 29.5° using a program CELDIM (EnrafNonius, 1989): a = 5.6906(4), b = 17.061(1), c =9.732(1) Å, V = 944.9(1) Å3, a: b: c = 0.3335: 1:0.5704. Data reduction was done using the programs REFCAL and SORTRF and analyticalabsorption correction using LSABS from theXtal3.2 package (Hall et al., 1992). The structure
was solved in the space group Pnma by direct
methods with program GENTAN from the Xtal3.2
package. The structure (without hydrogen atoms)
was refined on F2 with program LSLS from theXtal3.2 package using all 1407 observed uniquereflections (Rint = 0.085) weighted 1/σ2. The secondary-extinction correction was done according
to Becker & Coppens (1974) with the extinction
parameter g = 6004(538). The refinement converged to R = 0.086, Rw = 0.046 and Goof = 1.06
with 83 parameters, including anisotropic-displacement parameters. The largest residuals in the
difference-Fourier map are -3.81 and 4.17 e/Å3.

Crystal structure
Atom coordinates, standardized by the program STRUCTURE TIDY (Gelato & Parthé,1987), and equivalent isotropic-displacement
parameters for non-hydrogen atoms are given in
Table 3, and a list of selected interatomic distances
is given in Table 4. Atom coordination and bondvalences were analyzed by the program IVTON

Table 3. Atom positions and displacement parameters for rollandite.

Table 4. Selected interactomic distances (Å) for rollandite.

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Table 5. Bond valence (vu) table for rollandite.

(Balić Žunić & Vicković, 1996). There are two Cu
and one As sites in the structure. Cu1 is coordinated by a distorted octahedron, Cu2 by a squarepyramid and As by a tetrahedron.
No hydrogen atoms were detected in the difference-Fourier map, therefore the concept ofbond valences (Brown & Kang Kun Wu, 1976)
was used to locate the hydrogen bonds. The data of
Brese & O’Keeffe (1991) were used to calculate
the bond valences for all non-hydrogen atoms(Table 5). The sums for O4 (0.53) and O7 (0.24)
indicate the presence of water molecules. The sumfor O6 (0) indicates the presence of a watermolecule not included in the coordination ofcations. The sums for all other oxygen atoms
range from 1.34 to 2.05, thus indicating that someof them may act as proton acceptors in H⋅⋅⋅Obonds. Valence sums for cations are in good agreement with their corresponding ionic charges.
Based on the dependence of H⋅⋅⋅O bondvalence on O⋅⋅⋅O distance (assuming stretched OH⋅⋅⋅O bond angles) according to Brown &Altermatt (1985) we propose possible hydrogenbonds. The results are given in Table 5. The watermolecule O6 yield two O-H and accept two H⋅⋅⋅Obonds. The water molecules O4 and O7 yields twoO-H bonds each. The atom O1 accepts three H⋅⋅⋅Obonds. From the six hydrogen bonds one is intralayer, and five are inter-layer.

according to the classification of Eby &Hawthorne (1993). It can be derived from a sheetof edge-sharing octahedra (as observed in brucite)
by removal of one half of the cations (every second cation pair is missing). The resulting (020)
sheet of Cu1O6 octahedra in rollandite can be seen

Discussion of the structure

Fig. 2. The structure of rollandite viewed approx. down[100]. The Cu1 octahedra are light grey, the Cu2 squarepyramids are medium grey and the As tetrahedra are indark grey. Hydrogen bonds are shown as black thicklines, the outlines of the unit cell are dashed.

The structure of rollandite (Fig. 2) belongs tothe group of M = M-T framework structures

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Fig. 3. The sheets of edge-sharing octahedra which arethe basic building units of rollandite parallel to (020).
The grey scale of the coordination polyhedra corresponds to Fig. 2.

in Fig. 3. Opposing the empty cation pair site,
alternatively on both sides of the sheet, there are
two AsO4 tetrahedra which share two vertices eachwith the sheet. The tetrahedra cross-link sheets via
the infinite chains of Cu2O5 square pyramids
extending along the a-axis by sharing one vertex
with the chain (Fig. 2). The sheets are additionaly
cross-linked by hydrogen bonds and by the interstitial water molecule O6H2 situated in the channels running along the a-axis.
The powder pattern of rollandite visuallyresemble that of a synthetic compound
Cu3(AsO4)2·4H2O (Mas, 1949) whose structure,
however, was not determined.
Acknowledgements: We thank C.M. Gramaccioli, M. Pasero and C. Chopin for their helpfulcomments and suggesting improvements, as wellas J. Wüest for the scanning electron microscope
photographs and C. de Jong Bozkurt for typing themanuscript.

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Received 6 March 2000
Modified version received 9 May 2000
Accepted 10 May 2000

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