Tobermorite

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Tobermorite
Torbermorite CSH 3D Crystal Structure RasMol.gif
Crystal structure of tobermorite: elementary unit cell viewed in 3D
General
Category Silicate mineral,
Calcium silicate hydrate
Formula
(repeating unit)
Ca5Si6O16(OH)2·4H2O, or;
Ca5Si6(O,OH)18·5H2O
Crystal symmetry Orthorhombic 2 2 2
Unit cell a = 11.17 Å, b = 7.38 Å, c = 22.94 Å; β = 90°; Z = 4
Identification
Formula mass 702.36
Color Pale pinkish white, white, brown
Crystal habit As minute laths; fibrous bundles, rosettes or sheaves, radiating or plumose, fine granular, massive.
Crystal system Orthorhombic - Disphenoidal
Cleavage {001} Perfect, {100} Imperfect
Mohs scale hardness 2.5
Luster Vitreous, silky in fibrous aggregates
Streak White
Diaphaneity Translucent to translucent
Specific gravity 2.423 - 2.458
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
References [1][2][3]
Not to be confused with torbernite, a hydrated copper uranyl phosphate.

Tobermorite is a calcium silicate hydrate mineral with chemical formula:

Ca5Si6O16(OH)2·4H2O

or

Ca5Si6(O,OH)18·5H2O

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 alteration mineral in metamorphosed limestone (e.g. in the Maqarin Area (North Jordan), or in Crestmore (Riverside County, California, USA)) and in skarn.

Tobermorite was first described in 1880 for an occurrence in Scotland, on the Isle of Mull, around the locality of Tobermory.[2]

Crystalline mass of tobermorite.

Use in Roman concrete[edit]

Aluminium substituted tobermorite is understood to be a key ingredient in the longevity of ancient Roman undersea concrete, as per the American Ceramic Society.[4]

See also[edit]

References[edit]

External links[edit]