Abstract

An unstable serpentine polymorph which exhibits the combined properties characteristic of a number of other known polymorphs is described. Macrocrystals of the mineral, from the Tilly Foster Mine, New York State, indicate that it is a six-layered monoclinic serpentine, with each successive layer displaced relative to its neighbours by ± a/3 and ± b/3 and, or, by a rotation of ±60°. Individual layers are further modulated periodically in the a crystal direction. The resulting crystal has superlattice controlled a and c parameters.

Finer fractions of a porvdered macrocrystal, observed by electron microscopy, show that it tends to break down into smaller, simpler units: thin corrugated plates are formed, which themselves part along weak corrugation joints, forming elongated rods. The formation of rods deprives the basic serpentine layers of the satisfactory strain relief mechanism attributed to corrugation. The rods are seen to compensate for this deprivation by curling parallel to their elongation, eventually producing more stable chrysotile-like tubes. The complete metamorphosis from plates to tubes has been followed by selected area electron difiraction.

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