Mineral Information and Data:

Aenigmatite
Na4(Fe2+10Ti2)O4[Si12O36] [CNMNC approved formula]

Named in 1865 from the Greek for riddle, apparently an allusion to its (formerly) uncertain chemical composition.

IMA status : Approved Species 1982 ()
CLASSIFICATION 
Dana
(8th edition) :
69.02.01a.01  
  (69) Inosilicate Chains with Side Branches or Loops
  (69.02) with P>2
  (69.02.01a) Aenigmatite and related species (Aenigmatite subgroup)
  
Nickel-Strunz
(10th edition) :
09.DH.45
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DH) with 4-periodic single chains, Si4O12
  
Crystal system: Triclinic System
Point group (H-M): 1 — pinacoidal
Unit cell: a = 10.406 Å, b = 10.813 Å, c = 8.926 Å, a = 104°56
Crystal Habit: Crystals long prismatic; twining common; lamellar
Twinning: By rotation ⊥ (011) or about [010] of the pseudomonoclinic cell; polysynthetic.
  
Color: Black
Diaphaneity: Translucent to opaque
Luster: Vitreous to greasy
Hardness (Mohs): 5.5
Measured Density: 3.74 to 3.85 g/cm3
Cleavage: 2; {010} and {100} good
Tenacity: Brittle
Fracture: Uneven
Streak: Reddish brown
  
Geologic Setting: A primary constituent in sodium-rich alkalic volcanics, pegmatites, and other silica-poor igneous rocks.
Mineral Association: Aegirine, augite, riebeckite, arfvedsonite, hedenbergite, fayalite, ilmenite
  

 

Aenigmatite
Origin: Mayor Island, New Zealand
Sample size: unknown
Photo: Evan Chugg

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