Portlandite , Ettringite Locality: Ettringer Feld, Kro. Mayen, Eifel, Germany Exposed in the Mineralogical Museum of University Bonn, Germany — Photo: Ra'ike · CC BY-SA 3.0
Portlandite
Natural calcium hydroxide — the calcium analogue of brucite, and the mineral that hardens Portland cement.
Intro adapted from Wikipedia (CC BY-SA).
Portlandite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Ca(OH)₂.
It crystallizes in the hexagonal crystal system (space group P-3m1). It is a member of the Brucite structural group.
Key properties: Mohs hardness 2; specific gravity 2.23; Pearly on cleavages luster; refractive index 1.561; optically uniaxial.
IMA symbol Por, grandfathered status — known before the IMA’s founding, named in 1933.
An alteration product of calcium silicates in larnite-spurrite contact metamorphic rocks (Scawt Hill, Ireland); in fumaroles (Vesuvius, Italy); as a precipitate from alkaline springs derived from ultramafic rocks (Jebel Awq, Oman).
It is found associated with Afwillite, calcite, larnite, spurrite (Scawt Hill, Ireland); calcite, halite (Jebel Awq, Oman); calcite, brownmillerite, hydrocalumite, mayenite.
The name refers to its relation to a principal hydrolysis product of Portland cement.