Yoga sutra 1.41
kṣīṇa-vr̥tter-abhijātasy-eva maṇer-grahītr̥-grahaṇa-grāhyeṣu tatstha-tadañjanatā samāpattiḥ
When the agitation settles, the mind becomes like a flawless transparent crystal.
Such a crystal has no colour of its own. It just reflects the colour of the objects around it. A tranquil mind is like a transparent crystal—it assumes the colour of whatever is in its proximity. Such is the case with the perceiver, the act of perceiving and the object perceived.
A tranquil mind then, is a mind that is no longer affected by its own modifications and remains clear and calm. A yogi/yogini with a crystal-clear mind lives in the world and yet remains unaffected by it.
Damian Cadman-Jones is an authorised teacher of Prana Vashya Yoga™