Opal is comfortable and it lacks "toughness." Hardness would be the resistance to currently being scratched, but toughness would be the resistance to breaking. If you do not fill your tumbler to ability, your opal can be tossed all around violently from the barrel. It only requires Particular glass polish, https://aluminumoxide54219.tusblogos.com/35123964/a-review-of-aluminum-oxide