Collection of forms resulting from all the combinations of the Platonic and Catalan polyhedra which characterize the m 3 5 icosahedral point group

Livio Zefiro
Dip.Te.Ris., Universita' di Genova, Italy
(E-mail address: livio.zefiro@fastwebnet.it)

Notes
  • Tested with Internet Explorer 7, Mozilla Firefox 3, Opera 9.64 and Google Chrome at 1024x768 and 1280x1024 pixels
  • All the images have been generated by SHAPE 7.0, a software program for drawing the morphology of crystals, distributed by Shape Software
  • Hovering with the mouse on each image, the symbol of a pointer appears: if your web browser is set up to visualize VRML files, by clicking with the left button of the mouse it should be possible to visualize in a new window the corresponding dynamic image, that can be enlarged, rotated, shifted... Cortona 3D Viewer is a good Web3D visualizer that can be downloaded from here: at present it is working also with the updated versions of the main browsers.

As already pointed out in two previous papers [1,2], all the icosahedral compound forms, and in particular the ones belonging to the holohedral m 3 5 point goup, can be derived from seven single forms, corresponding to two Platonic and five Catalan polyhedra.
The two Platonic polyhedra are the dodecahedron and the icosahedron: both are characterized by Miller's indices having a fixed value. The same holds true for the rhomb-triacontahedron, a Catalan polyhedron dual of a quasi-regular Archimedean polyhedron, the icosidodecahedron.
Conversely, the indices of the other four forms can assume variable values, in the intervals defined in the following table.

Miller's indices of the single forms characterizing the m 3 5 icosahedral point group

Forms of the m 3 5 icosahedral point group (golden ratio τ = 1.61803...)
{1τ0} dodecahedron
{τ 1/τ 0} icosahedron
{100} rhomb-triacontahedron
{hk0} triakis-icosahedron (where: 0 < k/h <1/τ2 )
{hk0} deltoidal hexecontahedron (where: 1/τ <h/k <τ2 )
{hk0} pentakis-dodecahedron (where: 0 < h/k <1/τ )
{hkl} hexakis-icosahedron (where: 0 < k/h <1/τ2l/h <1/τ - τk/h, with h > 0)

Miller's indices and names of the forms belonging to the m 3 5 point group.
One must remember that the indices of all the faces of a polyhedron with icosahedral symmetry can be obtained from the cyclic permutation of a unique set of indices only in case of the dodecahedron, whereas the sets of indices are two, three or five in case of the other six forms. Relatively to each form, only one set of indices is reported in the table.


Each group of isomorphic forms, characterized by variable indices, can be led to coincide with the corresponding archetypal Catalan polyhedron by the attribution of suitable values to the indices of the four forms:
All the 120 compound forms derived from the two Platonic and the five Catalan polyhedra are here represented, grouped in six sets; an equal distance from the centre of each solid has been attributed to all the faces of the compound forms.
Taking into account that the hexakis-icosahedron is the only icosahedral form belonging uniquely to the m 3 5 point group (whereas the other six forms are compatible also with 235, the other icosahedral point group, which is lacking in mirrors and centre of inversion), the first set includes the compound forms in which the hexakis-icosahedron is added to each combination of the other six single forms; it follows that the total number of such compound forms is 63 = 26-1
The remaining sets include:
The addition of these 120 compound forms to the 7 single forms leads to the overall 127 forms which characterize the m 3 5 point group (as it follows from 127 = 27-1).

(clicking on each following image by the left button of the mouse, one can visualize the corresponding VRML dynamic image)
The seven single forms which characterize the m 3 5 icosahedral point group and the 120 derived compound forms


The seven single forms
1) dodecahedron 2) icosahedron 3) rhomb-triacontahedron 4) triakis-icosahedron 5) deltoid-hexecontahedron 6) pentakis-dodecahedron 7) hexakis-icosahedron


The sixty-three compound forms which include a Catalan hexakis-icosahedron
Six compound forms made of two forms
6+7 5+7 4+7 3+7 2+7 1+7
Fifteen compound forms made of three forms
5+6+7 4+6+7 3+6+7 2+6+7 1+6+7
4+5+7 3+5+7 2+5+7 1+5+7 3+4+7
2+4+7 1+4+7 2+3+7 1+3+7 1+2+7
Twenty compound forms made of four forms
4+5+6+7 3+5+6+7 2+5+6+7 1+5+6+7 3+4+6+7
2+4+6+7 1+4+6+7 2+3+6+7 1+3+6+7 1+2+6+7
3+4+5+7 2+4+5+7 1+4+5+7 2+3+5+7 1+3+5+7
1+2+5+7 2+3+4+7 1+3+4+7 1+2+4+7 1+2+3+7
Fifteeen compound forms made of five forms
3+4+5+6+7 2+4+5+6+7 1+4+5+6+7 2+3+5+6+7 1+3+5+6+7
1+2+5+6+7 2+3+4+6+7 1+3+4+6+7 1+2+4+6+7 1+2+3+6+7
2+3+4+5+7 1+3+4+5+7 1+2+4+5+7 1+2+3+5+7 1+2+3+4+7
Six compound forms made of six forms
2+3+4+5+6+7 1+3+4+5+6+7 1+2+4+5+6+7 1+2+3+5+6+7 1+2+3+4+6+7 1+2+3+4+5+7
Compound form
made of seven forms

1+2+3+4+5+6+7


Thirty-one further compound forms including a Catalan pentakis-dodecahedron
Five compound forms made of two forms
5+6 4+6 3+6 2+6 1+6
Ten compound forms made of three forms
4+5+6 3+5+6 2+5+6 1+5+6 3+4+6
2+4+6 1+4+6 2+3+6 1+3+6 1+2+6
Ten compound forms made of four forms
3+4+5+6 2+4+5+6 1+4+5+6 2+3+5+6 1+3+5+6
1+2+5+6 2+3+4+6 1+3+4+6 1+2+4+6 1+2+3+6
Five compound forms made of five forms
2+3+4+5+6 1+3+4+5+6 1+2+4+5+6 1+2+3+5+6 1+2+3+4+6
Compound form
made of six forms
1+2+3+4+5+6


Fifteen further compound forms including the Catalan deltoid-hexecontahedron
Four compound forms made of two forms
4+5 3+5 2+5 1+5
Six compound forms made of three forms
3+4+5 2+4+5 1+4+5 2+3+5 1+3+5 1+2+5
Four compound forms made of four forms
2+3+4+5 1+3+4+5 1+2+4+5 1+2+3+5
Compound form
made of five forms
1+2+3+4+5


Seven further compound forms
including the Catalan triakis-icosahedron
Three compound forms made of two forms
3+4 2+4 1+4
Three compound forms made of three forms
2+3+4 1+3+4 1+2+4
Compound form
made of four forms
1+2+3+4


Three further compound forms
including the rhomb-triacontahedron
Two compound forms made of two forms
2+3 1+3
Compound form
made of three forms
1+2+3


Last compound form including
an icosahedron and a dodecahedron
Compound form
made of two forms
 
1+2


In order to obtain whichever icosahedral form starting from the previous 127 polyhedra, it is possible to vary:
  • the distance, from the centre of the solid, of the faces of each form belonging to a compound form
  • the indices of each Catalan polyhedron (with the exception of the rhomb-triacontahedron), leading to all its isomorphic polyhedra
  • the number of single forms, isomorphic of the Catalan polyhedra different from the rhomb-triacontahedron, which are concurrently present in a compound form.
Afterwards one can see three examples of compound forms (not involving Catalan polyhedra), together with the single forms whose intersection can generate such particular compound forms, in case of suitable distances, from the centre of the solids, of the faces of each single form.
In detail:
  • the compound form in the first row derives from the intersection of a triakis-icosahedron, an icosahedron and two different pentakis-dodecahedra
  • the compound form in the second row derives from the intersection of a rhomb-triacontahedron, an icosahedron and two different deltoid-hexecontahedra
  • the compound form in the third row derives from the intersection of a dodecahedron, a hexakis-icosahedron and two different triakis-icosahedra.
The compound form on the left derives from the intersection of the four single forms on the right: a triakis-icosahedron, an icosahedron and two different pentakis-dodecahedra.
The compound form on the left derives from the intersection of the four single forms on the right: a rhomb-triacontahedron, an icosahedron and two different deltoid-hexecontahedra
The compound form on the left derives from the intersection of the four single forms on the right: a dodecahedron, a hexakis-icosahedron and two different triakis-icosahedra.

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