What is the main index for gold?

The HUI Index and the Philadelphia Gold and Silver Index (XAU) are the two most watched gold indices in the market. The main difference between them is that the HUI index only takes into account the stocks of gold producers, while the XAU index includes both gold and silver producers. The two main differences between them are that the NYSE Arca Gold BUGS Index tracks gold mining stocks exclusively, while the XAU index tracks companies involved in gold and silver mining, and includes companies that cover their production beyond 18 months.