The lodestone, made from a piece of magnetite, which is naturally magnetic, was vital in the early centuries of navigation to ensure that the ship's compass worked properly. Until the mid-18th century, when improved compasses were developed, compass needles lost their magnetism quite quickly and had to be re-magnetised by stroking a lodestone along the needle's length.

Lodestones were often mounted in cases of brass, bronze or silver, and sometimes had an iron or steel keeper - a bar to help preserve their magnetic power. This lodestone has a silver frame with a suspension ring on top, and is 'armed' with two pieces of steel at the bottom. It is held in a shaped sharkskin-covered case. The magnetic poles are at the side and are indicated by 'N' and 'S' on the frame.