Gyrolite and reyerite from ’S Airde Beinn, northern Mull

Abstract
Summary: Reyerite is found in close association with gyrolite in the metamorphic aureole of the volcanic plug of 'S Airde Beinn, northern Mull, and has apparently been formed by metamorphism of the gyrolite. The gyrolite, with a composition close to Ca16Si24O60(OH)3.14H2O, closely approaches trigonal symmetry with a 9·76±0·02 Å and c 3 × 22·26±0·1 Å; biaxial with a small 2V and α 1·537, β 1·547, γ 1·549. The reyerite is trigonal with a 9·76±0·02 Å, c 19·10±0·04 Å and space group Pω 1·568 and ε 1·563, and the unit cell contains about 14 atoms of Ca, 24 of Si (with some substitution by 4(OH)−), and 14H2O as (OH)− and H2O.

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