What does the cryptic crossword clue "Rock I'd found in Bosnia after explosion (8)" mean?

The definition is "Rock". The wordplay uses an anagram. anagram of I'D + BOSNIA = OBSIDIAN; definition: "Rock" The answer is OBSIDIAN.

Rock I'd found in Bosnia after explosion (8)

Daily Mail Cryptic #16459 | 29 Across | 2020-12-02 flower