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Grains of Infinity are created by setting Bedrock on fire and letting it burn out naturally. Provided that the fire burns for long enough, there is a 50% chance of it spawning Grains of Infinity. Sometimes the fire burns out to quickly, so the actual chance is slightly under 50%.
Grains of Infinity are not fire proof. They do survive a little longer that most items, but they can be destroyed by fire.
If Fire Ticks are disabled, Ender IO will cause fires on Bedrock to burn out after a certain amount of time.
Starting fires automatically is easy to do using a vanilla Dispenser and a redstone clock, Observer, or Block Detector. Vanilla Dispensers only use a Flint and Steel if the block in front of them is air or TNT, otherwise they do nothing.