Mineral Information and Data:

Armstrongite
CaZrSi6O15 • 2.5H2O [CNMNC approved formula]

Named for Neil Alden Armstrong, (1930-), American astronaut, first human being on the moon.

IMA status : Approved Species 1973 (IMA1972-018)
CLASSIFICATION 
Dana
(8th edition) :
72.05.04.01  
  (72) Phyllosilicate Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings
  (72.05) with corrugated and complex layers
  (72.05.04) Elpidite/armstrongite
  
Nickel-Strunz
(10th edition) :
09.EA.35
  (09) Silicates
  (09.E) Phyllosilicates
  (09.EA) Single nets of tetrahedra with 4-, 5-, (6-), and 8-membered rings
  
Crystal system: Monoclinic System
Point group (H-M): 2 — sphenoidal
Unit cell: a = 14.04Å, b = 14.16Å, c = 7.81Å β = 109.55°
Crystal Habit: Crystals up to 2 cm and in aggregates
Twinning: polysynthetic by rotation about [100]
  
Color: Dark to pale brown
Diaphaneity: Semitransparant
Luster: Vitreous
Hardness (Mohs): 4.6
Measured Density: 2.56 to 2.59 g/cm3
Cleavage: 2; {001} perfect, {100}good
Tenacity: Very brittle
Streak: Brownish white
  
Geologic Setting: In schlieren of alkalic granite pegmatite, at the contact of arfvedsonite granite with xenoliths of felsic volcanic rocks.
Mineral Association: Quartz, microcline, albite, aegirine, arfvedsonite, monazite, synchesite, titanite, other titanosilicates
  

 

Armstrongite
Large brown crystals to 6 mm in pegmatite matrix (XRD confirmed)
Origin: Khan-Bogdinskii Massif, Mongolia (type locality)
Sample size: 5 x 4 x 4 cm
Photo: Tom Loomis

 

Armstrongite
(zoom-in of above)

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