What is "rasalingam"

In Hinduism, Rasalingam or Parad Lingam is a Lingam, the symbol of the god Shiva, made of mercury. Tamil Siddhas carved Shiva Lingam from solidified mercury. The process of solidification of mercury is the secret process enunciated by Tamil Siddhas. In Tamil, mercury is called Pada-rasam and the Shiva Lingam made using pada-rasam is called Rasalingam. In Sanskrit, mercury is called Parad and the Shiva Lingam made using parad is called Parad Lingam. Rasalingams or Parad Lingams are consecrated in Hindu Shiva temples, Ashrams and other places of worships.