Coal In My Garden

My grandfather recently passed away and I was able to keep a large piece of coal (Yes, a large "lump" of coal) that he personally mined for when he was a kid. I was wondering if it would be an okay idea to display this large piece of coal in my garden as a tribute to him, but I am not sure how this could affect the flowers I already have planted. I currently have Marigolds, Petunias, and roses planted.
I am a beginning gardener so all feedback would be appreciated! Thank you!

This sounds like a great idea and important to you.  Coal is carbon. I doubt if there will be a problem. I think it is a safe bet to gamble on the impurities.   The most common one would be sulphur which is an element commonly added to gardens to make them more acid.

Hi Libby, welcome to Permies!

I think that piece of coal is pretty cool. Coal is ancient organic matter, and if it were mine I'd put it in my garden!

Yeah, I'd have no worries. Coal is just concentrated ancient organic matter in the first place.

In fact, leonardite coal is a fairly common soil additive, as it's oxidized to basically pure humic acid.

Awesome! Thank you all so much! I can't wait to find the perfect spot for it now!

Frosts will split it up into pieces over time if you get them in your area.