The largest ETF that invests in silver has rallied 20% in August to handily outperform gold prices.

The iShares Silver Trust (NYSEArca: SLV) is up 20.1% for the month, compared with a gain of 6.2% for SPDR Gold Shares (NYSEArca: GLD). [Silver ETFs Leading August Surge in Precious Metals]

The outperformance of silver is a bullish sign for precious metals, writes Hubert Moolman at SilverSeek.

However, the silver ETF was on track for a loss this week after rising the past three weeks. [Silver ETFs Getting Help From Speculators]

The amount of silver held in SLV has been rising recently after the ETF saw outflows through most of 2013. [Silver ETF Holdings Highest Since April After 20% Rally]

iShares Silver Trust

Full disclosure: Tom Lydon’s clients own SLV and GLD.