Favored mineral

A favored mineral was a gem or precious metal, which was favored by a deity.

Description
Deities could show their powers through major manifestations and minor manifestations. The appearance of a gem (or a mineral) fell into the latter category.

These stones were made to appear by deities to inform mortals of something. This could be something as general as pleasure or displeasure. But also something concrete like the existence of an infiltrator.

The ways in which these gems could provide information were varied. For example, Selûne could make a moonstone shine for a brief moment to be made seen by a follower of hers, telling the same that a fellow follower was in the vicinity, while Baervan Wildwanderer showed his favor by letting his followers find high quality emeralds while the same were either of poor quality or even crumbled away when he wanted to show his displeasure, and Berronar Truesilver could tarnish silver to end a warning.

Mortals' Reaction
Mortals sacrificed such gems and minerals to their deities and consecrated them.