Stauraxonia homopola : Appended Forms



Homopola scalenoidea


(Forms looking like more or less regular bipyramids, but with a non-planar equatorial plane




The Homopola scalenoidea are bipyramidal forms. But they lack mirror planes (except the Scalenoidea rhomboedra and dimera), in particular mirror planes parallel to the main axis. They possess, however, 2-fold rotation axes perpendicular to the main axis. All this causes the equatorial plane to be non-planar.


Although no Organisms are to be expected to have realized Homopola scalenoidea, several crystals (from the Tetragonal and Hexagonal Systems) represent this basic form in several (promorphological) species. These species are represented by the following promorphological categories :







      











First Species of the Scalenoidea



Scalenoidea sextamera



(Hexagonal trapezohedra)







The Scalenoidea sextamera are based on geometric bodies called Hexagonal Trapezohedra. The symmetry content of such bodies is :   
6 2 2, which corresponds to the Hexagonaltrapezohedric Crystal Class of the Hexagonal Crystal System.

We can consider a hexagonal trapezohedron as consisting of six antimers (each involving two of its faces) grouped around the main axis.

See for details and Figures HERE.


When you came from the document treating of the Promorphology of Crystals, and when you want to go back to it, click HERE, or click the back button of your browser.    
















Second Species of the Scalenoidea



Scalenoidea quadrimera



(Tetragonal trapezohedron)







The Scalenoidea quadrimera are based on geometric bodies called Tetragonal Trapezohedra. The symmetry content of such bodies is :   
4 2 2, which corresponds to the Tetragonal-trapezohedric Crystal Class of the Tetragonal Crystal System.

The tetragonal trapezohedron can be viewed as consisting of four antimers (each involving two of its faces) grouped around the main axis.

See for details and Figures HERE.


When you came from the document treating of the Promorphology of Crystals, and when you want to go back to it, click HERE, or click the back button of your browser.    




















Third Species of the Scalenoidea



Scalenoidea trimera



(Trigonal Trapezohedron)







The Scalenoidea trimera are based on geometric bodies called Trigonal Trapezohedra. The symmetry content of such bodies is :   
3 2, which corresponds to the Trigonal-trapezohedric Crystal Class of the Hexagonal Crystal System.

See for details and Figures HERE.


When you came from the document treating of the Promorphology of Crystals, and when you want to go back to it, click HERE, or click the back button of your browser.















Fourth Species of the Scalenoidea



Scalenoidea rhomboedra



(Rhombohedron)







The Scalenoidea rhomboedra are based on geometric bodies called Rhombohedra. The symmetry content of such bodies is :   
3* 2/m, which corresponds to the Ditrigonal-scalenohedric Crystal Class of the Hexagonal Crystal System.

The Rhombohedron can be viewed as a (more or less) pyramidal form consisting of three antimers (each involving two of its faces) grouped around the main axis. To obtain a rhombohedron one can deform a cube in the direction of one of the axes of 3-fold rotoinversion, i.e. one of the axes that run through two of the cube's opposite corners (vertices).

See for details and Figures HERE.


When you came from the document treating of the Promorphology of Crystals, and when you want to go back to it, click HERE, or click the back button of your browser. 















Fifth Species of the Scalenoidea



Scalenoidea duomera



(Rhombic Bisphenoid)







The Scalenoidea duomera are based on geometric bodies called Rhombic Bisphenoids, or Rhombic Tetrahedra. The symmetry content of such bodies is :   
2 2 2, which corresponds to the Rhombic-bisphenoidic Crystal Class of the Orthorhombic Crystal System.

The Rhombic Bisphenoid can be viewed as a (more or less) pyramidal form consisting of two antimers (each involving two of its faces) grouped around the main axis. In fact we have to do with a 2-fold bipyramid in which the constituent single pyramids are rotated with respect to each other. Because of the two-foldness the faces meet in a line instead of in a point (two faces meet in a line at the top, and two, in a line, at the bottom).

See for details and Figures HERE.


When you came from the document treating of the Promorphology of Crystals, and when you want to go back to it, click HERE, or click the back button of your browser.















Sixth Species of the Scalenoidea



Scalenoidea dimera



(Tetragonal Bisphenoid)







The Scalenoidea dimera are based on geometric bodies called Tetragonal Bisphenoids, or Tetragonal Tetrahedra. The symmetry content of such bodies is :   
4* 2 m, which corresponds to the Tetragonal-scalenohedric Crystal Class of the Tetragonal Crystal System.

The Tetragonal Bisphenoid can be viewed as a (more or less) pyramidal form consisting of two antimers (each involving two of its faces) grouped around the main axis. In fact we have to do with a 2-fold bipyramid in which the constituent single pyramids are rotated with respect to each other. Because of the two-foldness the faces meet in a line instead of in a point (two faces meet in a line at the top, and two, in a line, at the bottom).

See for details and Figures HERE.


When you came from the document treating of the Promorphology of Crystals, and when you want to go back to it, click HERE, or click the back button of your browser.




 
 
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