The cones of Hang Va have many features of raft cones. These calcite rafts form as a thin layer on the surface of cave pools. They sink into the pool either under their own weight when they grow too thick, or when hit by a drop of water falling from the cave roof. A repeated drip from the same place sinks a number of rafts that then build up on the pool floor to create a cone, which may reach to the level of the water surface. These are known as raft cones, because they are cones formed from calcite rafts.
Steep sided cones are more often called tower cones. It is not known exactly why some cones form very steeply, and other with a more shallow slope.
A striking feature of the tower cones in Hang Va, and those in many other caves, is the external layer of calcite that gives them a knobbly appearance and also hides any structure remaining from the original piles of rafts.
The knobbly outer surface and very steep profiles of the cones in Hang Va are similar to the features of tufa towers. These form over vents of geothermally warmed water, full of dissolved calcite, that lie in the floors of lakes and cause rapid, underwater precipitation of the calcite. Again they are exposed only when the lake level declines. Those of Lake Abhé in Djibouti are the best known examples (Waltham, 2005). Many of these rise to heights of more than 20m.
Features comparable to tufa towers but formed inside caves are known as geysermites.
The one available cross-section of a cone from Hang Va reveals a porous core with upward-pointing branches, a structure that would be expected in a growing tufa tower, or geysermite.