https://github.com/Gerold55/MineClone-2-Textures
https://forum.minetest.net/viewtopic.php?t=16407
https://github.com/minetest/minetest_game/tree/master/mods/default/textures
flint - https://github.com/MysticTempest/REFI_Textures/blob/master/textures/default_mcl_core/stone/default_flint.png
gravel - https://github.com/minetest-texture-packs/Good-Morning-Craft/blob/master/default/default_gravel.png
bubble - https://github.com/Gerold55