Good Day;

How can one determine if corundum Crn formed by mineral-related hydrothermal alteration, or by contact metamorphism ?
A heavy mineral concentrate has clear crystal chips in 3 colours, and grains of gritty-well included brn Crn, maybe with andalusite.

Does dehydration of diaspore form brn 'gritty' granular Crn? Or is that texture typical of Crn formed by metamorphism of argillites?

The location in S British Columbia is next to a Cretaceous granitic contact, the paleo P from other studies ~2.5-3.5 Kb max, & max. temp ~500 deg C. Trace cordierite scheelte & hercynite spinel also occur ...

What might microprobe analysis show? How does Crn from meta-carbonates differ from that of argillites, or that of 'advanced argillic alteration'?

Bill Howard in Calgary Canada

available photo: HM-18 Corundum c gns 1 to 20 ed.jpg