Category Sulfate mineral Strunz classification 7.BC.15 Space group I4132 | Formula(repeating unit) Ca4(AlO2)6SO4 Crystal system Isometric | |
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Crystal class Gyroidal (432)H-M Symbol: (432) | ||
Ye'elimite is the naturally occurring form of calcium sulfoaluminate, Ca4(AlO2)6SO4. It gets its name from Har Ye'elim in Israel in the Hatrurim Basin west of the Dead Sea where it was first found in nature.
The mineral is cubic, with 16 formula units per unit cell, and a cell dimension of 1.8392 nm, and is readily detected and quantified in mixtures by powder x-ray diffraction.
Occurrence in cement
It is alternatively called "Klein's Compound", after Alexander Klein of the University of California, Berkeley, who experimented with sulfoaluminate cements around 1960, although it was first described in 1957 by Ragozina. Ye'elimite is most commonly encountered as a constituent of sulfoaluminate cements, in which it is manufactured on the million-tonne-per-annum scale. It also occasionally occurs adventitiously in Portland-type cements. On hydration in the presence of calcium and sulfate ions, it forms the insoluble, fibrous mineral ettringite, which provides the strength in sulfoaluminate concretes.
It is manufactured by heating the appropriate quantities of finely-ground alumina, calcium carbonate and calcium sulfate to around 1000-1100°C, preferably in the presence of small quantities of fluxing materials. On heating above 1350°C, it begins to decompose to tricalcium aluminate, calcium oxide, sulfur dioxide and oxygen.