Some believe, that you can destroy a diamond by immersing it in an acid. You can use a hammer and break it all up in tiny pieces, but you haven't destroyed it.
Step2
To truly destroy it, you heat it to over 800 degrees with oxygen present.
Step3
It will break down the carbon bonds and there will be no diamond molecules left.
Tips & Warnings
Find someone who is knowledgeable enough to help you complete this project.
Think twice and maybe a few more times. That is a diamond!