River cobbles of all different shapes were stored in the ship's hold to enhance stability. Wooden sailing vessels were inherently buoyant, and tall masts made them extremely top-heavy. Ballast stones were added or removed as the weight of cargo, supplies, or ordnance changed. Anchors and extra cannon were also sometimes used as ballast.
The most common rock type present in the ballast stones recovered from the Queen Anne's Revenge shipwreck is basalt. An igneous rock not unlike gabbro, which was also found on the ship, basalt is an abundant rock that would have likely been in plentiful supply for those seeking ballast for ships like Queen Anne's Revenge.
Chert, less commonly used. This sedimentary rock is often found with sharp edges. For that reason, it was often used to build tools and weapons. In this case, chert was used simply for its weight; one among a myriad of stones used to regulate the ship's ballast at sea.
Felsic volcanics like the one shown here are also common. They are generally composed of plagioclase and quartz.
Gabbro, less commonly used. This igneous rock constitutes much of the oceanic crust of the Earth. Known for its density, this rock was helpful to sailors in that it provided considerable weight to the ship's ballast relative to its size.
Granite, less commonly used. A mainstay among igneous rocks, this type of stone would be in fairly plentiful supply at the time Queen Anne's Revenge was delivered. Of course, it may have been taken aboard the ship on subsequent voyages rather than provided at the outset of its construction, as needs for ballast changed depending on sailing conditions and water depth.
Limestone, less commonly used. A sedimentary rock consisting mainly of calcium carbonate, limestone is formed in a variety of circumstances, which means it could have been found near many of Queen Anne's Revenge's ports of call. It had many uses during this period, but this particular stone most likely served as ballast.
Quartz, less commonly used. A varied mineral, quartz was dense enough to justify use as as serviceable ballast aboard Queen Anne's Revenge. It would have been found in deposits of granite and sedimentary rock, which were also found in the remains of Queen Anne's Revenge's ballast hold on the sea floor.