Mineral Information and Data:

Alleghanyite
Mn2+5(SiO4)2(OH)2 [CNMNC approved formula]

Named after its locality: Bald Knob, Alleghany Co., North Carolina, USA.

IMA status : Valid species (Pre-IMA 1932) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
52.03.02b.01  
  (52) Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O
  (52.03) with cations in [6] coordination only
  (52.03.02b) Humite group (Chondrodite series)
  
Nickel-Strunz
(10th edition) :
09.AF.45
  (09) Silicates
  (09.A) Nesosilicates (Isolated tetrahedron) structures
  (09.AF) Nesosilicates with additional anions; cations in [4], [5] and/or only [6] coordination
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 8.275 Å, b = 4.850 Å, c = 10.720 Å, b = 104.64°
Crystal Habit: Crystals slender plate-like, deeply striated by twinning or unstriated stout platy crystals; usually massive or irregular grains.
Twinning: On {001}, lamellar, common; also on {105}, {305}
  
Color: Brown to pinkish brown to deep pink
Diaphaneity: Transparent to translucent.
Luster: Vitreous to dull.
Hardness (Mohs): 5.5
Measured Density: 4.02 g/cm3
Tenacity: Brittle
Fracture: Conchoidal
  
Polymorphism and Series: Dimorphous with ribbeite; forms a series with chondrodite.
Geologic Setting: Hydrothermally deposited, in lenses in a manganese-bearing vein (Bald Knob, North Carolina, USA); in veins crosscutting franklinite ore near pegmatites in a metamorphosed stratiform Zn-Mn deposit (Franklin, New Jersey, USA)
  

 

Alleghanyite
Pink crystalline grains in an area of 10 x 5 mm
Origin: Langban mine, Varmland, Sweden (type locality)
Sample size: 5 x 4 x 1.5 cm
Photo: Tom Loomis

 

Alleghanyite
(zoom-in of above)

 

Alleghanyite
Origin: Sterling Hill mine, Ogdensburg, Sussex County, New Jersey, U.S.A.
Sample size: 6 x 3.5 x 3.5 cm
Photo: Rob Lavinsky

 

Alleghanyite
(zoom-in of above)

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