# Two Polyhedra Derived From the Icosahedron

The polyhedron above is a zonish icosahedron, with zones added to that Platonic solid based on its faces and vertices. Its faces are twenty equilateral triangles, thirty equilateral decagons, and sixty rhombi. After making it, I used faceting to truncate the vertices where sets of five rhombi met, creating the polyhedron below. It has twelve regular pentagons as faces, with the sixty rhombi of the polyhedron above turned into sixty isosceles triangles, along with the thirty decagons and twenty triangles from the first of these two polyhedra. This second one could be called either a faceted zonish icosahedron, or a truncated zonish icosahedron.

Both of these polyhedra were created using Stella 4d: Polyhedron Navigator, software you can try for free at http://www.software3d.com/Stella.php.

# Zonohedra, Zonish Polyhedra, and Another Puzzle

In a recent post, I showed many images of zonohedra, then challenged readers to figure out, from the images, what zonohedra are: polyhedra with only zonogons as faces. Zonogons, I then explained, are polygons with (A) even numbers of edges, and with opposite edges always (B) congruent and (C) parallel. Here is another collection of zonohedra. (Individual images may be enlarged with a click.)

The next set of polyhedra shown, below, are not true zonohedra (as all the ones above are), but merely “zonish polyhedra.” From examination of the pictures above and below, can you figure out the difference between zonohedra and zonish polyhedra?

When you are ready to see the solution to the puzzle, simply scroll down.

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While zonohedra have only zonogons as faces, this restriction is “loosened” for zonish polyhedra. Such solids are formed by zonohedrifying non-zonohedral polyhedra, and letting at least some of the faces of the resulting polyhedra remain non-zonogonal. Zonish polyhedra  are called “zonish” because many (usually most) of their faces are zonogons, but not all of them — in each case, some non-zonogonal polygons (such as triangles and/or pentagons, with their odd numbers of edges) do appear. Non-zonogonal polygons are not required to have odd numbers of edges, of course: simply having opposite edges be parallel, but of different lengths, is enough to prevent a polygon (such as a hexagon, octagon, or decagon) from being a zonogon.

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Software credit: I used Stella 4d to make these images. This program may be tried for free at this website.

# A Zonish Polyhedron with 522 Faces, Together with Its 920-Faced Dual The polyhedron above is a 522-faced zonish polyhedron, which resembles, but is not identical to, a zonohedron. True zonohedra are recognizable as that type of polyhedron by their exclusively zonogonal faces. Zonogons are polygons with even numbers of sites, and with opposite sides both congruent and parallel. If you examine the polyhedron above carefully, you’ll find it does not follow these rules. Stella 4d, the polyhedral-manipulation software I use to make these images, allows one to create either a true zonohedron, or a mere “zonish” polyhedron, as the user chooses, starting from another polyhedron (which may, itself, be zonish, a true zonohedron, or neither).

The next polyhedron is the dual of the polyhedron above. This dual has 920 faces. The duals of both zonohedra and zonish polyhedra have a distincive appearance, but, to my knowledge, no one has yet given either set of polyhedra a single-word name. In my opinion, such names are both needed, and deserved. If you would like to try Stella 4d for yourself, there is a free trial download available at http://www.software3d.com/Stella.php.

# The Seven Zonish Dodecahedra with Zones Added Based on Faces, Edges, and/or Vertices

If a zonish dodecahedron is created with zones based on the dodecahedron’s vertices, here is the result. If the same thing is done with edges, this is the result — an edge-distorted version of the great rhombicosidodecahedron. Another option is faces-only. Although I haven’t checked the bond-lengths, this one does have the general shape of the most-symmetrical 80-carbon-atom fullerene molecule. Also, this shape is sometimes called the “pseudo-truncated-icosahedron.” The next zonish dodecahedron has had zones added based on the dodecahedron’s faces and edges, both. Here’s the one for vertices and edges. Here’s the one for faces and vertices. Finally, the last of this set of seven has had zones added based on all three: faces, vertices, and edges. All seven of these were made with Stella 4d, which is available at http://www.software3d.com/Stella.php.

# The Seven Zonish Icosahedra with Zones Added Based on Faces, Edges, and/or Vertices

If a zonish icosahedron is created with zones based on the icosahedron’s vertices, here is the result. If the same thing is done with edges, this is the result. Another option is faces-only. The next zonish icosahedron has had zones added based on the icosahedron’s faces and edges, both. Here’s the one for vertices and edges. Here’s the one for faces and vertices. Finally, the last of this set of seven has had zones added based on all three: faces, vertices, and edges. All seven of these were made with Stella 4d, which is available at http://www.software3d.com/Stella.php.

# A Polyhedral Journey, Beginning with Face-Based Zonohedrification of an Icosahedron

To begin this, I took an icosahedron, and made a zonish polyhedron with it, with the new faces based on the zones of the existing faces. Here’s the result. Next, I started stellating the polyhedron above. At the sixth stellation, I found this. It’s a true zonohedron, and the first polyhedron shown here is merely “zonish,” because one has triangles, and the other does not. (One of the requirements for a polyhedron to be a zonohedron is that all its faces must have an even number of sides.) After that, I kept stellating, finding this as the 18th stellation of the first polyhedron shown here. With this polyhedron, I then made its convex hull. At this point, the irregular hexagons were bothering me, so I used Stella 4d‘s “try to make faces regular” option. (Stella 4d is polyhedron-manipulation software you can try for free, or purchase, right here.) The next step I chose was to augment all the yellow trapezoids with prisms, each with a height 1.6 times the trapezoids average edge length. The next step was, again, to make the convex hull. At this point, I tried “try to make faces regular” again, and was pleased with the result. The green rectangles became so thin, however, that I had to stop displaying the edges and vertices, in order for then to be seen. Next, I augmented both the blue faces (decagons) and the yellow faces (dodecagons) with antiprisms, again using a height 1.6 times that of the augmented faces’ average edge-lengths. Next, I made the convex hull again — a step I often take immediately after augmenting a polyhedron. This one surprised me, as it is more complicated than I expected. To clean things up a bit, I augmented only the trapezoids (dark pink) with prisms, and dodecagons (green) with antiprisms, again using the factor 1.6 for the augmentation-height. The next step I chose was to take the convex hull, once more. I had not yet noticed that the greater height of the trapezoidal prisms would cause the dodecagonal antiprisms to be “lost” by this step, though. Next, “try to make faces regular” was used again. This last result had me feeling my polyhedral journey was going in circles, so I tried augmentation again, but in a different way. I augmented this polyhedron, using prisms, on only the red trapezoids (height factor, 1.6 again) and the blue rectangles (new height factor, 2.3 times average edge length). After that, it was time to make another convex hull — and that showed me that I had, indeed, taken a new path. I found the most interesting faces of this polyhedron to be the long, isosceles trapezoids, so I augmented them with prisms, ignoring the other faces, using the new height-factor of 2.3 times average edge length this time. Of course, I wanted to see the convex hull of this. Who wouldn’t? I then started to stellate this figure, choosing the 14th stellation as a good place to stop, and making the edges and vertices visible once more. # A Zonish Icosahedron, and Some of Its “Relatives”

To begin this, I used Stella 4d (available here) to create a zonish polyhedron from the icosahedron, by adding zones along the x-, y-, and z-axes. The result has less symmetry than the original, but it is symmetry of a type I find particularly interesting. After making that figure, I began stellating it, and found a number of interesting polyhedra in this polyhedron’s stellation-series. This is the second such stellation: This is the 18th stellation: The next one, the 20th stellation, is simply a distorted version of the Platonic dodecahedron. This one is the 22nd stellation: This is the 30th stellation: The next really interesting stellation I found was the 69th: At this point, I returned to the original polyhedron at the top of this post, and examined its dual. It has 24 faces, all of which are quadrilaterals. This is the third stellation of this dual — and another distorted Platonic dodecahedron. This is the dual’s 7th stellation: And this one is the dual’s 18th stellation: At this point, I took the convex hull of this 18th stellation of the original polyhedron’s dual, and here’s what appeared: Here is this convex hull’s dual: Stella 4d, the program I use to make these (available here), has a built-in “try to make faces regular” function. When possible, it works quite well, but making the faces of a polyhedron regular, or even close to regular, is not always possible. I tried it on the polyhedron immediately above, and obtained this interesting result: While interesting, this also struck me as a dead end, so I returned to the red-and-yellow convex hull which is the third image above, from right here, and started stellating it. At the 19th stellation of this convex hull, I found this: I also found an interesting polyhedron as the 19th stellation of the dual which is three images above: ## Faced-Based Zonish Versions of the Icosahedron and the Icosidodecahedron

### Image I’ve had some success lately finding near-misses to the Johnson solids by making face-based zonish versions of various polyhedra. These were found during that search, and are certainly not near-misses, but I still find them interesting, primarily due to their symmetry. Like the others, they were found using Stella 4d, which you can try or buy at http://www.software3d.com/Stella.php.

The top image was formed by making this modification to the icosahedron, and the one below (which you can enlarge with a click) was created by doing the same thing to an icosidodecahedron. ## The Seven Zonish Rhombicosidodecahedra Based On Symmetry Axes

### Image The top image here is of a zonish polyhedron based on adding zones along the five-fold symmetry axes of a rhombicosidodecahedron. All its edges are the same length, and its 62 faces include thirty elongated octagons, twelve regular pentagons, and twenty triangles. All of its edges have the same length.

The edges of this next polyhedron are also all of the same length. It was made in the same way, except that zones were added along both three- and five-fold symmetry axes of a rhombicosidodecahedron. Its 182 faces include thirty elongated dodecagons, twenty triangles, twelve regular pentagons, sixty squares, and sixty rhombi. If only the three-fold symmetry axes are used to make a zonish polyhedron from a rhombicosidodecahedron, this next polyhedron, also with all edge lengths equal, is the result. It also has 182 faces, and they are of the same type as in the one immediately before, except that thirty elongated octagons replace the dodecagons from that polyhedron. A rhombicosidodecahedron also has two-fold symmetry axes. If only those axes are used to make a zonish rhombicosidodecahedron, this next polyhedron is the result:  a modified form of the great rhombicosidodecahedron, with unequal edge lengths. If the two- and three-fold symmetry axes are both used, the result, once again, is a 182-faces polyhedron, but it also has unequal edge lengths, and none of its faces are regular polygons. It is shown below. There are twelve decagons, sixty rectangles, sixty hexagons of one type, twenty hexagons of another type,  and thirty octagons. Another possible combination is to use the two- and five-fold symmetry axes to create a zonish rhombicosidodecahedron. This yields a polyhedron with 122 faces, with all except the sixty squares being irregular. The other faces are twelve decagons, thirty octagons, and twenty hexagons: Finally, there is one last combination — using the two-, three-, and five-fold symmetry axes, all at once. Here’s what it looks like: As one should expect, this produces a zonish polyhedron with more faces than any of the earlier ones shown above: 242 in all. As in the last one shown, only the sixty squares are regular, although the sixty pink hexagons are at least equilateral. There are also sixty rectangles, twenty hexagons of a second type, thirty dodecagons, and twelve decagons.

All of these zonish rhombicosidodecahedra were created using Stella 4d, software available at http://www.software3d.com/Stella.php.