It's raining diamonds on Neptune & Uranus

Alec Muzzy writes "The U of C of Berkeley has reported that on Neptune the intense heat and pressure of the atmosphere likely creates diamonds out of methane which then fall like hail on the gas giant. " Interesting reasons why - but isn't it a Arthur C. Clarke book that postulates, back in the 80s, that the center of of the gas giants are enormous diamonds - like the size of the earth?