Portlandite
Image: <a href="//commons.wikimedia.org/w/index.php?title=User:Krissu89&action=edit&redlink=1" class="new" title="User:Krissu89 (page does not exist)">Kristjan Leben</a> (CC BY 4.0)
Mineral NamePortlandite
Chemical FormulaCa(OH)2
Mohs Hardness2.5
Crystal Systemhexagonal
Lustervitreous
Streak Colorwhite
Cleavageperfect on {0001}
Fractureuneven
Specific Gravity2.23
Colorswhite, colorless, pale yellow, pale green
Transparencytransparent
Type LocalityScawt Hill, Northern Ireland (natural); common in cementitious materials globally
Mineral GroupHydroxides
Usescement chemistry, industrial processes, research
Associated Mineralscalcite, aragonite, ettringite, gypsum
Raritycommon
Description
The image shows microscopic, platy, hexagonal crystals of portlandite growing within a void in a porous matrix, as seen under a scanning electron microscope.
Geological Context
Portlandite is a key component in hydrated cement and concrete. It can also form naturally in contact metamorphic rocks (e.g., metamorphosed limestones) and hydrothermal veins, or as a secondary mineral in high-pH environments, such as the oil shale ash sediments shown.
