https://www.mindat.org/glossary/cuboctahedron  

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A geometric cuboctahedron is defined as a polyhedron with 8 triangular faces and 6 square faces. A cuboctahedron has 12 identical vertices, with 2 triangles and 2 squares meeting at each, and 24 identical edges, each separating a triangle from a square (source: Wikipedia).

Finding a true geometric cuboctahedron in nature is extremely rare: in most cases the 24 edges are not identical. Nevertheless some crystals come close to this geometric polyhedron, as illustrated here by the photo of the Okoruso fluorite.

In mineralogy, a cuboctahedron is the name for a crystal that shows the combination of two isometric crystal forms: the cube {100} and the octahedron {111}. The size of both forms does not matter: as long as both are present, the crystal will be called a cuboctahedron. The cuboctahedron can be seen in many minerals that belong to the isometric system, including fluorite, galena and pyrite.

Since in mineralogy a cuboctahedron does (need to) not have 24 identical edges, it comes in two major habits:

* smaller four-sided faces and larger six-sided faces (because the octahedron is dominant)

* larger eight-sided faces and smaller three-sided faces (because the cube is dominant) 

When the octahedron is slightly dominant over the cube, a cuboctahedron can also be confused with a cubododecahedron. 

See this discussion for ways to distinguish between both: 
https://www.mindat.org/mesg-523029.html

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