Mineral Information and Data:

(Mn2+,Ca)4(Al,Mg,Mn3+)6(AsO4)(SiO4)2(Si3O10)(OH,O)6 [CNMNC approved formula]

Named in 1872 for the locality - Salmchâteau, in the Ardennes, Belgium. Renamed to ardennite-(As) with the discovery of ardennite-(V).

IMA status : Renamed IMA Approved; 2007 ()
(8th edition) :  
  (58) Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups
  (58.03) with insular single and triple groups (n=1,3)
  (58.03.01) Ardennite group
(10th edition) :
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BJ) Sorosilicates with Si3O10, Si4O11, etc. anions; cations in octahedral [6] and greater coordination
Crystal system: Orthorhombic System
Point group (H-M): mmm (or 2/m 2/m 2/m) — dipyramidal
Unit cell: a = 8.7126 Å, b = 18.5124 Å, c = 5.8108 Å
Crystal Habit: Individual crystals are rare. Crystals prismatic, acicular; crystalline aggregates and small rosettes of tapered acicular crystal
Color: Yellow to yellowish brown, black
Diaphaneity: Nearly opaque, translucent in thin splinters
Luster: Subadamantine
Hardness (Mohs): 6 - 7
Measured Density: 3.69 - 3.75 g/cm3
Cleavage: 2; {010} perfect, {110} distinct
Tenacity: Brittle
Fracture: Subconchoidal to uneven
Streak: Pale brownish yellow
Geologic Setting: In pegmatites and quartz veins in schist (Salmchateau, Belgium); in highly oxidized Mn, Al-rich metasediments (Andros Island, Greece).
Mineral Association: Quartz, albite, pyrolusite, piemontite, spessartine, braunite, hematite
Comments: Valid Pre-IMA 1872; Renamed to ardennite-(As) in 2007 with the discovery of ardennite-(V).


Slender prismatic, yellow crystals to 4mm embedded in quartz matrix.
Origin: Arrow Junction, Central Otago, New Zealand
Sample size: 2 x 1 x 1 cm
Photo: Tom Loomis


(zoom-in of above)