Mineral Information and Data:

Alumohydrocalcite
CaAl2(CO3)2(OH)4 • 3H2O [CNMNC approved formula]

Named in 1926 in allusion to the composition, containing ALUMinium, water (HYDRated) and a calcium carbonate (CALCITE) component.

IMA status : Approved Species 1980 ()
CLASSIFICATION 
Dana
(8th edition) :
16b.02.03.01  
  (16b) Carbonates - Hydroxyl or Halogen
  (16b.02) where (A)m (B)n (XO3)p Zq · x(H2O), with (m+n):p=3:2
  (16b.02.03)
  
Nickel-Strunz
(10th edition) :
05.DB.05
  (05) Carbonates and Nitrates
  (05.D) Carbonates with Additional Anions, with H2O
  (05.DB) With large and medium-sized cations
  
Crystal system: Triclinic System
Point group (H-M): 1 — pinacoidal
Unit cell: a = 6.498 Å, b = 14.457 Å, c = 5.678 Å, a = 95.83°, b = 93.23°, g = 82.24°
Crystal Habit: Chalky masses of fibrous crystals
  
Color: White to pale blue, yellowish, gray, violet
Diaphaneity: Transparent to opaque
Luster: Vitreous to pearly, earthy
Hardness (Mohs): 2.5
Measured Density: 2.23 - 2.40 g/cm3
Cleavage: 2; {100} perfect, {010} imperfect
Streak: White
  
Geologic Setting: Formed at low temperature by the action of carbonated waters on allophane or dickite in dolomites and limestones; chromian varieties are typically formed near altering chromite from serpentinites.
Mineral Association: Allophane, dickite, gibbsite, gypsum, aragonite, barite, Fe–Mn oxides
  
Other Properties: H2O Soluble.

 

Alumohydrocalcite
Spherical aggregates of white alumohydrocalcite crystals on matrix
Origin: Steinburch Kalem, Birresborn, Eifel, Germany
Sample size: 1 x 2 cm
Photo: Diederik Visser

 

Alumohydrocalcite
Fine micro white crystals, compact and indiscernible
Origin: South Bay, Scoroborough, Yorkshire, England
Sample size: 4 x 2 x 1 cm
Photo: Tom Loomis

 

Alumohydrocalcite
(zoom-in of above)

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