XAU - The Philadelphia Gold and Silver Index http://www.investinganswers.com/financial-dictionary/stock-market/philadelphia-gold-and-silver-index-2990 What it is: The Philadelphia Gold and Silver Index (Nasdaq: XAU) is traded on the Philadelphia Stock Exchange and is made up of 16 precious metal mining companies. How it works/Example: The Philadelphia Gold and Silver Index is made up of gold and silver mining company stocks and is not to be confused with physical gold and silver. Though the component stocks change in value daily, the updated list of companies in the index and their values can be found here. Why it Matters: The Philadelphia Gold and Silver Index is one of the most closely followed gold indices on the market. An investor can use this index as a benchmark to compare with his/her investments in gold or silver mining companies An investor can mirror the performance of this index by weighting their portfolio allocation similarly to the index's allocation. Alternatively, an investor may choose to invest in an ETF that trades gold and silver mining companies.