Mineral Information and Data:

Offretite
KCaMg(Si13Al5)O36 • 15H2O [CNMNC approved formula]

Named for Albert Jules Joseph Offret (1857-?), professor in the Faculty of Sciences, Lyon, France. First published in 1890. Approved and defined per nomenclature for zeolite minerals (IMA, 1997).

IMA status : Approved Species 1997 ()
CLASSIFICATION 
Dana
(8th edition) :
77.01.02.04  
  (77) Tectosilicate Zeolite group
  (77.01) true zeolites
  (77.01.02) Chabazite and related species
  
Nickel-Strunz
(10th edition) :
09.GD.25
  (09) Silicates
  (09.G) Tektosilicates with Zeolitic H2O
  (09.GD) Chains of 6-membered rings - tabular zeolites
  
Crystal system: Hexagonal System
Point group (H-M): 6m2 (or 6m2) — ditrigonal-dipyramidal
Space group: P6m2
Unit cell: a = 13.291(2)Å, c = 7.582(6)Å, Z=1
Crystal Habit: Crystals form hexagonal prisms, which may be hollow, vertically striated, to 3 mm; in hemispherical forms with radiating structure. Typically in complex overgrowths on erionite and levyne.
  
Color: Colorless to white
Diaphaneity: Transparent to translucent
Hardness (Mohs): 4
Measured Density: 2.13 g/cm3
Cleavage: {0001}, distinct
Tenacity: Brittle
Fracture: Uneven
  
Geologic Setting: Lining cavities in basalt.
Mineral Association: Zeolites, especially erionite, levyne, celadonite, montmorillonite.
  

 

Offretite
Colorless elongated hexagonal prisms in vug.
Mineral identification confirmed by a single-crystal X-ray diffraction
and chemical analysis.
Origin: Vinarice, Kladno, Czech Republic.
Photo: © RRUFF Project

 

Offretite
(zoom-in of above)

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