It looks like an eye of a cat. Cats eye is a stone that is favored by Ketu. Wearing this gem depends on the placement of Ketu in the Lagna Chart. Never wear Catâ€™s Eye (Lahasunya) without consulting an Astrologer.
Benefits : By wearing this gem one is able to subdue his enemies and is able to remove the effect of any negative forces working on him. This gives one social recognition and sudden spurts of growth. It protects from Erratic income and bestows stability in life. This is the gem of Moksha and frees one from the cycles of life and death.
Finger : worn in Middle Finger (Madhyama)
Metal : worn in PanchDhatu or Silver
Day : depends on Lagna Chart