Mineral Information and Data:

Beidellite
(Na,Ca)0.3Al2(Si,Al)4O10(OH)2 • nH2O [CNMNC approved formula]

Named for Beidell, Colorado, USA.

IMA status : Valid species (Pre-IMA 1925) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
71.03.01a.01  
  (71) Phyllosilicate Sheets of Six-Membered Rings
  (71.03) with 2:1 clays
  (71.03.01a) Smectite group (Dioctahedral Smectites)
  
Nickel-Strunz
(10th edition) :
09.EC.40
  (09) Silicates
  (09.E) Phyllosilicates
  (09.EC) Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: C2/m
Unit cell: a = 5.179Å, b = 8.970Å, c = 17.57Å, β = 90°
Crystal Habit: As thin plates, laths, and ribbons, to 30 μm; in veinlets filling fractures and as claylike masses.
  
Color: White, reddish brown, brownish gray
Diaphaneity: Translucent
Luster: Waxy to vitreous
Hardness (Mohs): 1 - 2
Measured Density: 2-3 (depending on hydration) g/cm3
Cleavage: Perfect on {001}
  
Geologic Setting: A constituent of bentonitic clays; an alteration product in hydrothermal mineral deposits, especially porphyry Cu-Mo systems; in soils derived from mafic rocks.
Mineral Association: Plagioclase, quartz, orthoclase, montmorillonite, kaolin, allophane, muscovite
  
Comments: Positive identification of minerals in the smectite group may need data from DTA curves, dehydration curves, and X-ray powder patterns before and after treatment by heating and with organic liquids.

 

Beidellite
Spherical aggregates of rose beidellite with chabazite and montmorillonite
Origin: Rupsroth, Kleinsassen, Rhön, Germany
Sample size: 2.5 x 3 cm
Photo: Diederik Visser

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