Hi Carl,

 

Based on everyone else’s responses supporting cordierite this study may be of use to you:

 

Cordierite and its retrograde breakdown products as monitors of fluid-rock interaction during retrograde path metamorphism: case studies in the Schwarzwald and the Bayerische Wald (Variscan belt, Germany) – Dissertation

Jörn C. Ogiermann

 

 

It’s available online as a downloadable pdf. If you can’t access it let me know.

 

cheers

 

 

Dear metamorphic community,

 

    We're working on a suite of archean paragneiss (Opinaca subprovince, Superior Craton) that display a barrovian-type sequence of isograds (bt-gt-st-sill). In the field, we have noticed a blueish-greenish mineral in the pressure shadows of early kinematic staurolite, and thought it's either chlorite or cordierite. However, in thin section, the mineral has clearly been altered and shows a heterogeneous chemical composition (see attached document for pictures and probe analyses).

 

We are looking for ways to confirm or infirm that the altered mineral was once cordierite. 

 

Any comments/advice/references will be greatly appreciated.

 

Best regards

 

Carl and Myriam