EMERALD

The ruling planet of this Gem/Stone is MERCURY (Wednesday)

What you have to do:

Donate - Emerald or another fine green gem, small green lentils, a green  pumpkin, a goat, or green clothes to a poor student on Wednesday At noon.

Fasting - On Wednesday, especially during Mercury transits and major or minor  Mercury periods Mantra.

Mantra - "Aum bram brim braum sah budhaya namah." To be chanted on Wednesday, two hours after sunrise, especially during major or minor Mercury periods.

This will help pleading Mercury (Budha) help in increasing health and intelligence