High volatility isn't going away for bitcoin, raising questions about whether the digital currency can be a sustainable investment asset. Late Saturday, the crypto-currency plunged 15 percent from nearly $6,500 to a low of $5,507, before intermittently shooting back up to near $6,400, according to CoinDesk. Bitcoin last traded near $6,060, down about 4 percent on the day. Trading in a U.S. stock index is typically halted after such an extreme drop, not to mention repeated swings higher or lower. However, more than 120 "cryptofunds" have emerged to invest in bitcoin, other digital currencies and related business ... (full story)