There is no question of animal bone. As I have already told you, Ivory Jewels, conchshell and cow dung are all pure. Everything is pure when employed in the service of the Lord. Just like the mrdanga kohl is made of skin and still it is held as pure. If you want more karatalas and mrdangas, you can contact Jayapataka Swami here in Calcutta (3, Albert Road; Calcutta-17, INDIA). So coral and mother of pearl are all right. Many Deities are made of coral.
Letter to Govinda Dasi, 28 May, 1971