325 is not an uncommon mark. It is an industry standard mark. It refers to the percentage of gold in the alloy. In this case it 32.5% (by weight) gold. This translates into 8kt gold. The other metals in this alloy are traditionally copper with a small percentage of silver.
If you want to know more -
There are a number of excellent books on jewellery making that contain all the alloying information and have charts for hallmarks and equivalents.
Gemology online just do a google search - its free to join and it has a separate section for jewellery. Many of the members are professionals that work in the industry.
