Panna Stone is the Gemstone of planet Mercury. Its ruling God is Lord Ganesha. 
Before wearing an Panna Ring it should be immersed in Pure Desi Ghee on a Tuesday evening. It should be left there for at least 8 hours. After this on Wednesday morning it should be taken out from the Ghee and washed with Gangajal mixed with saffron. 

Then wear this Panna Stone within 2 hours of sunrise after chanting Om! Braam Breem Broom Sah Budhai Namah 108 times. Emerald should be worn in Right Hand Little finger or as a pendant. In certain cases it is also suggested to be worn as a waist band. 

Panna like all Gemstones, is valued according to its Color, Cut, Clarity and Crystal. Emerald is the grass-green type of Beryl. 

Normally, in the grading of Gemstones, color is by far the most important criterion. However, in the grading of Emerald, crystal is considered a close second. Both are necessary conditions. A fine emerald must possess not only a pure vibrant green hue, but also a high degree of transparency to be considered a top Gemstone. 

If we talk about emerald in hindi then we find the name like Panna. 

Panna Stone