Bitcoin falls 30 percent, posts worst week since 2013

By Jemima Kelly and Gertrude Chavez-DreyfussNEW YORK/LONDON (Reuters) - Bitcoin plunged by 30 percent to below $12,000 on Friday as investors dumped the cryptocurrency after its sharp rise to a peak close to $20,000 prompted warnings by experts of a bubble.It capped a brutal week that had been touted as a new era of mainstream trading for the digital currency when bitcoin futures debuted on CME Group Inc , the world's largest derivatives market on Sunday.Friday's fall bled into the U.S. stock ma