The short answer is no. There is misinformation widely available that coal is believed to be the source of diamonds.
Rarely, if ever, has coal played a role in the production of diamonds. In fact, the majority of diamonds that have been discovered and dated are actually older than the first plants on Earth, which as we know is the source of coal.
Four mechanisms are believed to be responsible for the vast majority of natural diamonds found at or near the Earth’s surface and these processes rarely – if ever – involve coal.