fossilised oyster , pearl. 化石牡蠣 ， 珍珠。

150-million-year-old oyster which is ten times normal size probably contains the world's biggest pearl - but no-one wants to open it to find out | Mail Online http://www.dailymail.co.uk/sciencetech/article-2178655/150-million-year-old-oyster-times-normal-size-probably-contains-worlds-biggest-pearl--wants-open-out.html