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
– Aluminum-substituted 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 mineralhttps://en.wikipedia.org/wiki/Tobermorite