the oxygen, and the silicon is in 4-fold tetrahedral coordination around the oxygen. Around each silicon there is one OH group and there are three oxygens that neighbor them. The silicon tetrahedra are arranged so that they share an edge with calcium(1), and silicon(2) shares edges with the calcium(2) and calcium(3) polyhedral. The silicon tetrahedra are held together by the OH group and hydrogen bonding occurs between the hydrogen in the OH and the silicon tetrahedra. Hydrogen bonding is caused because the positive ion, hydrogen, is attracted to negatively charge ions which, in this case, are the silicon tetrahedra. Occurrence in concrete Afwillite is one of the calcium silicate hydrates (C-S-H) that form when Portland cement sets to form hardened cement paste (HCP) in concrete. The cement gets its strength from the hydration of tri- and di- calcium silicates (C3S and C2S) present in the clinker. See also List of minerals Other calcium silicate hydrate (C-S-H) minerals: Gyrolite Jennite Thaumasite Tobermorite Other calcium aluminium silicate hydrate (C-A-S-H) minerals: Tacharanite References Calcium minerals Cement Concrete Nesosilicates Hydrates Geology of Riverside County, California Crestmore Heights, California Monoclinic minerals Minerals in space group 9