To understand what "elvan rock" might refer to, we need more information. Could you please provide the following:
* Location: Where did you hear this term? (e.g., a specific region, country)
* Context: How was the term used? (e.g., in a geological study, a local description, a tourist brochure)
* Any other information: Did you see a physical sample of the rock? What did it look like?
With more information, it might be possible to determine what "elvan rock" refers to.
It's also possible that "elvan rock" is a mispronunciation or misspelling of a different geological term.
Let me know if you can provide any more details, and I'll do my best to help you understand.
