A mineral and mineral group name for a class of hydrated calcium silicate minerals with a strong resemblance to clay minerals, including variability of basal spacing with H₂O content, specific surface area, crystallinity, cation exchange (especially with Al substitutions), and polytypism. For example, tobermorite 9Å (chemical composition of Ca₅Si₆O₁₆(OH)₂), tobermorite 11Å (general formula of Ca_4+xSi₆O_15+2x(OH)_2-2x ^. 5H₂O), and tobermorite 14Å (Ca₅Si₆O₁₆(OH)₂ ^. 7H₂O; = plombièrite) refer to variations in basal spacings (d(002) values) and different degrees of hydration, which by successive heat treatments ultimately result in progressive dehydration (= “normal” tobermorite) to tobemorite 9Å. Some tobermorite 14Å samples do not dehydrate and are referred to as “anomalous”. Clinotobermorite also topotactically dehydrates upon heating to tobermorite 9Å. Tobermorites have sheets of 7-fold coordinated Ca polyhedra parallel to the (001) and silicate wollastonite-like tetrahedral chains, which link adjacent sheets in tobermoreite 9Å, forming parallel to the b axis (Merlino et al., 1999). The tetrahedral chains form double-width chains in tobermorite 11Å and clinotobermorite, and the double-width chains form zeolitic-type sites for Ca and H₂O. Tobermorite is found in hydrothermal altered carbonates (skarns) and basalt vesicles. The tobermorite group is important in cement hydration. Other hydrated calcium silicate phases are also important in cement formation, including an amorphous cement gel (e.g., Ca₃SiO₅ and cation substituted forms). Other hydrated calcium silicate minerals include jennite (Ca₉Si₆O₁₈H₂(OH)₈ ^. 6H₂O) and metajennite, riversideite (?Ca₅Si₆O₁₆(OH)₂), and foshagite (Ca₄Si₃O₉(OH)₂).
See calcium silicate hydrate (CSH) in Part 1