(1) http://ar-yoga.com/2011/10/bija-mantras-the-sounds-of-the-chakras-lam-vam-ram-yam-ham-om/
(2) https://www.the-open-mind.com/how-ancient-cultures-used-healing-crystals-stones-1/
(6) https://chopra.com/articles/10-powerful-mudras-and-how-to-use-them