Well. All of us are aware that Rayaru will come and bless us from where ever we call Him (Karedallige Baruva) right? Mrittika is one of the form to invoke Him for worshiping. A small amount of Mrittika given by the the Peethadhipathi of Rayara Matha in a copper or silver box. Then that box will be placed in the Vrindavana and then sealed by rock glue. Thus it becomes Rayar Mrittika Vrindavana.