The grains of the parabolic dunes
"Sand" is generally made up of whatever eroded rock type is nearby, minus the most easily eroded (and windswept) components. Typically, dunes are made up of highly resistant quartz grains, like the stuff that blows off of white sand beaches, for example, or feldspar sands which are even more erosion resistant (in certain cases). There are also very soft white gypsum sands in New Mexico who owe their existence to a nearby, inexhaustible supply of gypsum evaporites.

As for limestone sands, I've never heard of it although it's certainly possible given very specific circumstances. Nevertheless, that's not what controls dune morphology. Dune shape is almost entirely controlled by both wind and sand supply and similarly shaped dunes will occur regardless of grain composition if dune-forming components are the same.