Mineralpedia Details for Tobermorite

Tobermory, on the Island of Mull in Scotland, is the namesake and type locality for the mineral Tobermorite. It occurs as aproduct of hydrothermally altered calcium carbonate rich rocks, as well as a product of metamorphism. It will sometimes fill cavities in basaltic rocks.  Tobermorite is actually a group name that includes the 9-Å, 10-Å, 11-Å, and 14-Å hydrates. Tobermorite 11-Å is the group member actually called Tobermorite, whereas Tobermorite 9-Å is riversideite, Tobermorite 10-Å is oyelite, and Tobermorite 14-Å is plombierite. Occasionally, some Tobermorite 11-Å, Tobermorite, will shrink upon dehydration.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/tobermorite.pdf

Formula

Ca₅Si₆O₁₆(OH)₂·nH₂O 

Crystal System

Orthorhombic 

Crystal Habit

Fibrous, Aggregates, Radial 

Cleavage

Perfect, Imperfect, None 

Luster

Silky 

Color

white, light pink white, reddish white 

Streak

white 

Class

Orthorhombic - Disphenoidal 

Hardness

2.5 

WebMineral

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Mindat

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PXRD confirmed this to be structural type 14A of the Tobermoreite group. An incredibly complex group of minerals. Like almost everything else at Crestmore, it is a pearly white, platy calc-silicate. These crystals occur in radial bunches to about 1mm.