Note: Unstructured voxel blocks are unstructured blocks where the usual isotropic tetrahedral cells have been replaced by hierarchical
Cartesian cells (i.e. voxel cells). This type of block can therefore contain all the supported volume cell types (i.e. tetrahedra, pyramids, prisms, and
hexahedra). On the other hand, voxel blocks contain only hierarchical Cartesian cells (i.e. voxel cells).