Yantra is a nucleus of the visible and knowable, a linked diagram of lines by means of which visualized energies are concentrated. There are different kinds of Yantras and Sri-yantra is the Great Yantra. Other lesser yantras (Om yantra, Kali yantra etc.) are obliviously segments out of the all embracing Sru yantra. Yantras nay be made In permanent form of many substances. The most important is rock crystal. It’s clear colorless substances which can be shaped so as to focus light inclusive substance of fundamental reality just as colorless light includes all the possible colors of light. So crystal can serve as analogy for the substance which includes all substances.