Sur les Roches quarry, Bastogne, Luxembourg, Wallonia, Belgiumi

Regional Level Types
Sur les Roches quarry	Quarry
Bastogne	Municipality
Luxembourg	Province
Wallonia	Region
Belgium	Country

Sur les Roches quarry, Ardennes Mountains, Europe

Description: Acanthite occurs as fibrous radiating tufts of black crystals less than 100 µm in size, deposited on dendrites of native silver. The X-ray powder pattern is similar to that of synthetic acanthite (JCPDS 14-72). Qualitative chemical analysis confirms the presence of major Ag and S, together with minor Cu, Zn, and Cl.

Habit: lamellae up to a few centimetres

Description: "The most interesting geological site for biotite is the ensemble of veins in the Bastogne region, where the lamellae can be up to a few centimetres in length. Here, the mineral was baptised "bastonite". Already mentioned by A. Dumont (in Buttgenbach, 1947), it is considered to be an altered biotite. The chemical analysis was done by Klement (1888) and according to Corin (1930), some lamellae are reportedly titaniferous. The morphological and especially the optical characteristics of "bastonite" lead to its assimilation to biotite, a fact already suspected by J. Gosselet (Prinz, 1909). Therefore, the term "bastonite" should be abandoned." (Hatert et al., 2002)

Habit: lamellae up to a few centimetres

Description: "The biotite from Bastogne, particularly poor in potassium and rich in ferric iron and water, shows an enrichment in NH4+ (Darimont et al., 1988). An alteration of the mineral is evident by whitening and a variation in the optical axes angle. The X-ray powder diagram reveals a peak at 14Å, which could indicate a vermiculitisation phenomenon." (Hatert et al, 2002)

Description: Hatert et al. (2000): "Associated with altered galena, cerussite occurs as colourless to honey brown crystals with a greasy luster and a maximum size of 5 mm. Goniometric measurements on bipyramidal crystals clearly show the (110) pseudohexagonal twin. Depending on the development of the faces parallel to c, either an isometric facies or a prismatic one can be distinguished. Twinned crystals are frequent with the dominant forms {110}, {010}, {111} and {021}, less commonly associated with the forms {100}, {114} and {012}. Some less abundant isometric crystals, apparently not twinned, show the combination of the forms {100} {110} {130} {010} {111} {021}. It is the first occurrence of bipyramidal crystals in Belgium, which recalls the morphology of cerussite crystals from Mibladen, Morocco. Cerussite has been identified by X-ray diffraction whereas the chemical analysis showed minor Cu, Fe, Zn, Cd and Ni associated with Pb."

Colour: turquoise blue

Description: "The turquoise blue coatings of chrysocolla resemble wroewolfeite but can be distinguished by their conchoidal fracture. The mineral has been identified by X-ray diffraction and its composition confirmed by a chemical analysis. In addition to Si and Cu, Zn, Mn, Fe, Ca and S exist as minor elements." (Hatert et al., 2000).

Description: "Linarite forms fan-like aggregates of tiny tabular crystals up to 500 µm, and a light blue color. The mineral is closely associated with cerussite and chalcopyrite. X-ray powder data are similar to these of linarite from the Mammoth mine, Arizona, USA (JCPDS 30-493). Chemical analysis reveals major Cu, Pb and S with low proportions of Cl." (Hatert et al., 2000)

Description: Metallic flakes up to 5 mm with an irregular outline as disseminations on some samples of Siegenian quartzite.

Description: Dendritic aggregates up to 4-5mm associated with altered galena and acanthite. The aggregates are formed by entangled crystals among which two forms are observed: the cube {100} and the rhombododecahedron {110}. The identification of this mineral has been confirmed by chemical analysis which shows Ag with minor Cu, Zn, I, and Cl. The two last elements are probably related to the presence of halides such as iodargyrite, AgI, or chlorargyrite, AgCl.

Description: "The lead phosphate is closely associated with galena from which it derives by alteration. It occurs as microcrystalline apple green coatings on the inner side of some cavities in the quartz lenses. Viewed under the scanning electron microscope, the crystals, less than 50 µm in size, appear to be formed by a prism {1010} extended by curved faces. Qualitative chemical analysis shows major Pb, P and Cl with lower quantities of Ca, Cd and As." Hatert et al. (2000)

Habit: acicular

Colour: turquoise blue

Description: "Wroewolfeite exists as microcrystalline turquoise blue coatings of acicular crystals averaging 100 µm. X-ray powder pattern of this rare mineral agrees with that of wroewolfeite from Loudville mine, Massachusetts, USA (JCPDS 27-1133). Chemical analysis only confirms Cu and S." (Hatert et al., 2000)

Habit: prismatic, tabular, dipyramidal

Colour: orange

Description: Hatert et al. (2000): "Associated with altered galena and with pyromorphite, wulfenite occurs as isolated crystals up to 2 mm. They are orange-coloured, with a greasy luster. Crystals generally form very acute tetragonal dipyramids with curved faces unsuitable for goniometric measurements. Wulfenite crystallizes also as {101} tetragonal dipyramids, of which the orientation has been checked by X-ray diffraction. These crystals are sometimes modified by the forms {001} and {1k0}, with a relatively high k value difficult to determine with the classical goniometric methods. Both prismatic and tabular crystals exist. Some tabular crystals give the combination {100} {001}, sometimes modified by the small faces {101}. It is to be pointed out that tabular crystals of wulfenite, as well as crystals with {1k0} faces, had never been observed in Belgium so far. The parameters of the tetragonal unit-cell of wulfenite from Bastogne have been calculated from 26 reflections: a = 5.429(1) Å and c = 12.097(6) Å. These values correspond better with those given by Fransolet et al. (1977) for the wulfenite from Richelle than with those given by Hatert et al. (1998) for the wulfenite from Vielsalm. Chemical analysis shows Pb and Mo together with minor Fe and Cd. The presence of noticeable quantities of Fe and Cu into the lattice of the wulfenite from Vielsalm (Hatert et al 1998) could be responsible for the lower values of its unit-cell parameters when compared with these calculated for minerals from Bastogne and Richelle."