The three-dimensional shape depends upon how the fivelings are formed, including the environment such as gas pressure and temperature. In the very early work only pentagonal bipyramids were reported. In 1970 Ino tried to model the energetics, but found that these bipyramids were higher in energy than single crystals with a Wulff construction shape. He found a lower energy form where he added {100} facets, what is now commonly called the Ino decahedron. The surface energy of this form and a related icosahedral twin scale as the two-thirds power of the volume, so they can be lower in energy than a single crystal as discussed further below. However, while Ino was able to explain the icosahedral particles, he was not able to explain the decahedral ones.  Later Laurence D. Marks proposed a model using both experimental data and a theoretical analysis, which is based upon a modified Wulff construction which includes more surface facets, including Inos {100} as well as re-entrant {111} surfaces at the twin boundaries with the possibility of others such as {110}, while retaining the decahedral  point group symmetry. This approach also includes the effect of gas and other environmental factors via how they change the surface energy of different facets. By combining this model with de Wits elasticity, Archibald Howie and Marks were able to rationalize the stability of the decahedral to particles. Other work soon confirmed the shape reported by Marks for annealed particles. This was further confirmed in detailed atomistic calculations a few years later by Charles Cleveland and Uzi Landman who coined the term Marks decahedra for these shapes, this name now being widely used. 
The minimum energy or thermodynamic shape for these particles depends upon the relative surface energies of different facets, similar to a single crystal Wulff shape; they are formed by combining segments of a conventional Wulff construction with two additional internal facets to represent the twin boundaries. An overview of codes to calculate these shapes was published in 2021 by Christina Boukouvala et al. Considering just {111} and {100} facets:
* The Ino decahedron occurs when the surface energy of the {100} facets is small, ; 
* Common is the Marks decahedron with {100} facets and a re-entrant surface at the twin boundaries for 
* With  there is no {100} faceting, and the particles have been called nanostars.
* For very low  the equilibrium shape is a long rod along the common five-fold axis.
The photograph of an 0.5cm gold fiveling from Miass is a Marks decahedron with , while the sketch of Rose is for .  The 75 atom cluster shown above corresponds to the same shape for a small number of atoms. Experimentally, in fcc crystals fivelings with only {111} and {100} facets are common, but many other facets can be present in the Wulff construction leading to more rounded shapes, for instance {113} facets for silicon. It is known that the surface can reconstruct to a different atomic arrangement in the outermost atomic plane, for instance a dimer reconstruction for {100} facets of silicon particles of a hexagonal overlayer on the {100} facets of gold decahedra.
What shape is present depends not just on the surface energy of the different facets, but also upon how the particles grow. The thermodynamic shape is determined by the Wulff construction, which considers the energy of each possible surface facet and yields the lowest energy shape. The original Marks decahedron was based upon a form of Wulff construction that takes into account the twin boundaries. There is a related kinetic Wulff construction where the growth rate of different surfaces is used instead of the energies. This type of growth matters when the formation of a new island on a flat facet limits the growth rate. If the {100} surfaces of Ino grow faster then they will not appear in the final shape, similarly for the re-entrant surfaces at the twin boundaries -- this leads to the pentagonal bipyramids often observed. Alternatively, if the {111} surfaces grow fast and {100} slow the kinetic shape will be a long rod along the common five-fold axis as shown in the figure.
Another different set of shapes can occur when diffusion of atoms to the particles dominates, a growth regime called diffusion controlled growth. In such cases surface curvature can play a major role, for instance leading to spikes originating at the sharp corners of a pentagonal bipyramids, sometimes leading to pointy stars, as shown in the figure.