Tobermorite

Tobermorite
Crystalline mass of tobermorite
General
Category	Silicate mineral, Calcium silicate hydrate
Formula (repeating unit)	Ca5Si6O16(OH)2·4H2O, or; Ca5Si6(O,OH)18·5H2O
Strunz classification	9.DG.10
Crystal system	Orthorhombic
Crystal class	Disphenoidal (222) H-M symbol: (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 g/mol
Color	Pale pinkish white, white, brown
Crystal habit	As minute laths; fibrous bundles, rosettes or sheaves, radiating or plumose, fine granular, massive.
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

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 and in skarn. It has been reported from the Maqarin Area of north Jordan and in the Crestmore Quarry near Crestmore Heights, Riverside County, California.

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

Aluminium substituted tobermorite is understood to be a key ingredient in the longevity of ancient undersea Roman concrete, according to the American Ceramic Society.