Ardennite... made in Belgium...
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Ardennite (yellowish) on quartz. Salmchateau, Ardennes, Luxemburg, Belgium. Photo and collection H. Dillen. Field width about 25 mm. |
In 1872 a new mineral was recognised in a quartz vein in Salmchateau in the Ardennes massif, Luxemburg Province, Belgium. It was studied almost simultaneously by von Lasaulx, who gave it the name "ardennite", and Pisani, who named it "dewalquite", after G. Dewalque, a famous belgian geologist. After a real polemic, the name ardennite was finally adopted.
Untill 1922 Salmchateau was the only occurrence. Since then, ardennite has been identified at some other localities in Italy, India, Switzerland and elswhere, but the Salmchateau material is still by far the best available.
Ardennite has a very complex structure, related to that of orientite.
Here is the formula :
Mn4(Mg,Al,Fe)2Al4(As,V)O4(SiO4)2(Si3O10(OH)6
 | SEM-image of well formed terminated ardennite crystals.
Terminated crystals that you can observe visually are extremely rare. The largest crystal on this image is about 0.1 mm tall and 30 µm wide. The magnification factor was 1930X. |
Ardennite is orthorhombic. Its color can vary within all possibles shades of yellow to brownish. In the literature a relationship between the color (yellow versus orange) and the As/V ratio has been suggested, but this could not be confirmed by micro-analysis. The black color that occurs often is due to hematite inclusions.
The Salmchateau locality is closed for collecting since many years because high speed trains pass by the outcrop at a distance of about... 1 m !
Ardennite occurs in a second Belgian locality, Bihain, at a distance of a few kilometer from Salmchateau, but here the ardennite is extremely rare (actually limited to one or two pieces with micro-quantities of ardennite).
Other occurrences are localities in Italy, France, the United Kingdon, Greece, India and Japan.
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Working at the Salmchateau outcrop on July 24, 1971 : geologist Paul Plinke (with the hammer) and my wife Ria (sitting) - I took the picture.
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For those who are interested in detailed information, I have lots of literature (ancient and recent).
Just e-mail me