The ruling planet of this Gem/Stone is KETU (Thursday)

What you have to do:-

Donate - Donate a cat's eye gem, a brown cow with white spots, colored  blankets, or a dog to a poor young man on Thursday.

Fasting - On the first Thursday of the waxing moon, especially during major  Ketu periods.

Mantra -"Aum sram srim sraum sah ketave namah." To be chanted on Thursday at midnight, especially during major Ketu periods.

This will help pleading Ketu (Brihaspati) granting victory over enemies, favor from the King or Government, and reduction in diseases caused by Ketu.