Mineral Information and Data:

Amstallite
CaAl(Si,Al)4O8(OH)4 • (H2O,Cl) [CNMNC approved formula]

Named for the locality: Amstall graphite quarry, Amstall, Austria.

IMA status : Approved Species 1987 (IMA1986-030)
CLASSIFICATION 
Dana
(8th edition) :
72.01.04.01  
  (72) Phyllosilicate Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings
  (72.01) with 4-membered rings
  (72.01.04)
  
Nickel-Strunz
(10th edition) :
09.DP.25
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DP) Transitional ino-phyllosilicate structures
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 18.830 Å, b = 11.517 Å, c = 5.190 Å, b = 100.86°
Crystal Habit: As acicular prismatic crystals, to 1 cm, elongated and commonly striated ⊥ [001], with cross sections appearing rhombohedral or hexagonal.
  
Color: Colorless
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 3 - 5
Measured Density: 2.4 g/cm3
Cleavage: 1; {100} good
Tenacity: Brittle
Fracture: Conchoidal
Streak: White
  
Geologic Setting: In open fissures cutting pegmatitic schlieren, in hydrothermally altered graphite-bearing metamorphic rocks.
Mineral Association: Apatite, rutile, siderite, albite, laumontite, calcite, vivianite
  

<<< BACK TO MINERAL SEARCH