| Portlandite | |
|---|---|
| General | |
| Category | Oxide mineral |
| Chemical formula | Ca(OH)2 |
| Strunz classification | 04.FE.05 |
| Dana classification | 06.02.01.04 Brucite group |
| Crystal symmetry | Trigonal (3 2/m) - hexagonal scalenohedral |
| Unit cell | a = 3.589 Å, c = 4.911 Å; Z = 1 |
| Identification | |
| Color | Colorless, white to greenish white |
| Crystal habit | Hexagonal plates; commonly fibrous, powdery, massive. |
| Crystal system | Trigonal |
| Cleavage | Perfect on {0001} |
| Tenacity | Sectile with flexible cleavage plates |
| Mohs scale hardness | 2 |
| Luster | Pearly on cleavages |
| Diaphaneity | Transparent |
| Specific gravity | 2.23 |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.574 nε = 1.547 |
| Birefringence | δ = 0.027 |
| Solubility | Soluble in water producing an alkaline solution |
| Alters to | Alters to CaCO3 on exposure to CO2 bearing waters |
| References | [1][2][3][4] |
Portlandite is a rare oxide mineral, the naturally occurring form of calcium hydroxide (Ca(OH)2). It is the calcium analogue of brucite (Mg(OH)2).
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 larnite–spurrite. It occurs a 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.[1] It also occurs in the Kalahari manganese mining area of Kuruman, Cape Province, South Africa where it occurs as large crystals and masses.[2][1]
It occurs in association with afwillite, calcite, larnite, spurrite, halite, brownmillerite, hydrocalumite, mayenite and ettringite.[1]
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.[2][1]