Hydrotalcite: Properties and Occurrences

Hydrotalcite is a layered double hydroxide of general formula Mg6Al2CO3(OH)16·4(H2O), whose name is derived from its resemblance with talc and its high water content. It is a pearly-white mineral, consisting of hydrous aluminum and magnesium hydroxide and carbonate. It is a trigonal-hexagonal scalenohedral mineral containing aluminum, carbon, hydrogen, magnesium, and oxygen.

General Information

  • Category: Carbonate mineral
  • Formula: Mg6Al2CO3(OH)164(H2O)
  • Crystal system 3R polytype: Trigonal and 2H polytype: Hexagonal
  • Crystal class 3R polytype: Hexagonal scalenohedral (3m)

Fig: Hydrotalcite

Properties

The layers of the structure stack in multiple ways, to produce a 3-layer rhombohedral structure (3R Polytype), or a 2-layer hexagonal structure (2H polytype) formerly known as manasseite. The two polytypes are often intergrown. The carbonate anions that lie between the structural layers are weakly bound, so hydrotalcite has anion exchange capabilities.

  • Color: White with a possible brownish tint
  • Cleavage: {0001}, perfect
  • Tenacity: Flexible, not elastic
  • Mohs scale hardness: 2
  • Luster: Satiny to greasy or waxy
  • Streak: White
  • Diaphaneity: Transparent
  • Specific gravity: 2.03 – 2.09
  • Optical properties: Uniaxial (-)

Occurrence

It was first described in 1842 for an occurrence in a serpentine – magnesite deposit in Snarum, Modum, Buskerud, Norway. It occurs as an alteration mineral in serpentinite in association with serpentine, dolomite and hematite.

 

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