Thaumasite
Videos
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si6·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O.
Thaumasite (white) with prehnite (green) from Fairfax Quarry, Virginia
Group of thaumasite prisms from the Kuruman, Kalahari manganese fields, Northern Cape Province, South Africa (size: 4.2 × 3.1 × 1.2 cm)
Ettringite
Videos
Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2312·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically
Thaumasite
…Unlike conventional sulfate attack, in which the calcium hydroxide (portlandite) and calcium aluminate hydrates react with sulfates to form gypsum and ettringite (an expansive phase) respectively, in the case of the thaumasite form of sulfate attack (TSA) the calcium silicate hydrates ensuring the cohesion in…
Ettringite, Kalahari manganese fields, Northern Cape Province, South Africa
Ettringite, 6.5 × 3.2 cm. N'Chwaning Mines, Kalahari manganese fields, Northern Cape Province, South Africa
SEM image of fractured hardened cement paste, showing thin hexagonal plates of portlandite (calcium hydroxide) and needles of ettringite (micron scale)
Fibroradiated ettringite needles on slag (Concordia smelter, Eschweiler, Aachen, Germany)