Tobermorite is a calcium silicate hydrate mineral with chemical formula:
CaSiO(OH)·4HO or
CaSi(O,OH)·5HO.
Two structural varieties are distinguished: tobermorite-11 Å and tobermorite-14 Å.
Tobermorite occurs in hydrated cement paste and can be found in nature as an alteration mineral in metamorphosed limestone and in skarn. It has been reported to occur in the Maqarin Area of north Jordan and in the Crestmore Quarry near Crestmore Heights, Riverside County, California.
Tobermorite was first described in 1880 for an occurrence in Scotland, on the Isle of Mull, around the locality of Tobermory.