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Portlandite is an oxide mineral. It is the naturally occurring form of calcium hydroxide (Ca(OH)2) and the calcium analogue of brucite (Mg(OH)2).

Portlandite
Portlandite, Ettringite - Mineralogisches Museum Bonn.jpg
Portlandite and ettringite
General
CategoryOxide mineral
Formula
(repeating unit)
Ca(OH)2
Strunz classification4.FE.05
Dana classification06.02.01.04
Brucite group
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupP3m1
Unit cella = 3.589 Å, c = 4.911 Å; Z = 1
Identification
ColorColorless, white to greenish white
Crystal habitHexagonal plates; commonly fibrous, powdery, massive.
CleavagePerfect on {0001}
TenacitySectile with flexible cleavage plates
Mohs scale hardness2
LusterPearly on cleavages
DiaphaneityTransparent
Specific gravity2.23
Optical propertiesUniaxial (-)
Refractive indexnω = 1.574 nε = 1.547
Birefringenceδ = 0.027
SolubilitySoluble in water producing an alkaline solution
Alters toAlters to CaCO3 on exposure to CO2 bearing waters
References[1][2][3][4][5]

OccurrenceEdit

Portlandite occurs in a variety of environments. At the type location in Northern Ireland it occurs as an alteration of calc–silicate rocks by contact metamorphism of larnitespurrite. It occurs as fumarole deposits in the Vesuvius area. In Jebel Awq, Oman it occurs as precipitates from an alkaline spring emanating from ultramafic bedrock. In the Chelyabinsk coal basin of Russia it is produced by combustion of coal seams and similarly by spontaneous combustion of bitumen in the Hatrurim Formation of the Negev desert in Israel and the Maqarin area, Jordan.[2] It also occurs in the manganese mining area of Kuruman, Cape Province, South Africa in the Kalahari Desert where it occurs as large crystals and masses.[3][2]

It occurs in association with afwillite, calcite, larnite, spurrite, halite, brownmillerite, hydrocalumite, mayenite and ettringite.[2]

It was first described in 1933 for an occurrence at Scawt Hill, Larne, County Antrim, Northern Ireland. It was named portlandite because the chemical calcium hydroxide is a common hydrolysis product of Portland cement.[3][2]

ReferencesEdit

  1. ^ "Mineralienatlas - Fossilienatlas". www.mineralienatlas.de.
  2. ^ a b c d e "Handbook of Mineralogy" (PDF).
  3. ^ a b c "Portlandite: Mineral information, data and localities". www.mindat.org.
  4. ^ "Portlandite Mineral Data". www.webmineral.com.
  5. ^ Pallache, Charles; Berman, Harry; Frondel, Clifford (1944). The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana (7 ed.). Wiley. p. 641–642. ISBN 9780471192398.