Criteria for determining sequence (2a)

Plane-polarized light : Crossed polars

Here is a mutual association between muscovite and staurolite. Which came first? Consider these alternatives; which is more plausible?

1. A poikiloblast of staurolite is partially replaced by flakes of white mica (i.e. staurolite first).
2. A poikiloblast of staurolite grew within an aggregate of white mica flakes (i.e. muscovite first).

A lower magnification view (c. 1.2 cm across) of the texture is shown below. It should help to make the relationship more obvious.

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Created on ... October 4, 2003