Tobermorite

Subtopic: General Information Category: Silicate mineral, Calcium silicate hydrate Formula (repeating unit): (OH)4H2O, or; Ca(O,OH)5H2 IMA symbol: Tbm Strunz classification: 9.DG.10 Crystal system: Orthorhombic Subtopic: Identification Formula mass: 702.36 g/mol Color: Pale pinkish white, white, brown Mohs scale hardness: 2.5 Luster: Vitreous, silky in fibrous aggregates Specific gravity: 2.423 – 2.458 Subtopic: Crystal Structure Space group: C222 (no. 20) Unit cell dimensions: a = 11.17 Å, b = 7.38 Å, c = 22.94 Å; β = 90°; Z = 4 Cleavage: {001} Perfect, {100} Imperfect Streak: White Diaphaneity: Translucent to translucent Subtopic: Optical Properties Biaxial (+) Refractive index: nα = 1.570, nβ = 1.571, nγ = 1.575 Birefringence: δ = 0.005 Ultraviolet fluorescence: Fluorescent, Short UV: weak white to yellow, Long UV: weak white to yellow Subtopic: Use in Roman Concrete Aluminumsubstituted tobermorite is a key ingredient in ancient undersea Roman concrete Interaction with sea water causes crystalline structures to expand and strengthen Results in more durability compared to modern concrete in sea water Volcanic ash used by Romans contained phillipsite Tobermorite found in hydrated cement paste and in nature as an alteration mineral