(Source: London Evening Standard)
"a ring mate" ⇒ consider as "a ring" plus "mate"
General meaning ⇒ it's "the stone" ⇒ word for or name of a stone ⇒ a gemstone?
"a ring" ⇒ the shape of a ring? ⇒ i.e. the letter "o"
"mate" ⇒ another word for "mate" ⇒ e.g. "pal"
Answer ⇒ opal