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We have just launched a new range called Crystal Polydron. The size of the pieces are the same as our Original Polydron, the shapes are all solid and are totally transparent. They look stunning on light tables and against a light source. The introduction of transparent pieces allows you to see inside the structure.

We use the same language to describe uniform tilings and polyhedra: Platonic if all the regular polygons are the same, Archimedean if there's a mixture, and a tiling - like the kagome pattern, 3.6.3.6 - can be thought of as an infinite polyhedron. What controls the size of the polyhedron is the angular defect, d, the difference from 360°, at each vertex. They total 720°, so, if there are v vertices, vd = 720°.

In the case of our own planet the story begins around 4.3 billion years ago with the appearance of solid matter: ions joining to form crystals. We have to jump forward the same amount of time before organic life had evolved with the sophistication to discover their structures. Right up until the middle of the twentieth century this evidence was still indirect: we observed the scattering pattern when samples were bombarded by X-rays. But the electron microscope and its successors enabled us to identify individual ions. An important two-dimensional pattern discovered among minerals is the subject of this piece.

In order to test out some challenge activities I went to a local High School to run the first activity with a lower ability Year 8 class.

An unmarked regular tetrahedron has planes of symmetry. It does not therefore have left- and right-handed forms. (The technical word for handedness is chirality.) But here are nets for two tetrahedra in which each face has a different colour.

As part of the London Schools Excellence Fund, The Compton School in partnership with Finchley Catholic High School recently held two maths masterclasses for strong Year 6 mathematicians from schools in the Barnet and Haringey areas. They were ably supported by Year 8 students from the The Compton and Year 9 students from Finchley Catholic.

Most Sudoku puzzles use the numbers 1 to 9, but you can use anything – letters, colours, shapes, …And you can make up puzzles with fewer items. We shall use just 4. If you think such puzzles are likely to be too simple, I warn you that we shall move from 'single' Sudoku to 'double' Sudoku and even 'triple double' Sudoku.

Having built a polyhedron from a net or illustration, students will feel pleased with what they have done. But they can now capitalise on their success by finding the properties of their shape. Most important are the planes of mirror symmetry and axes of rotation symmetry. Then there is the matter of how many faces, edges and vertices they have. It is this second question which concerns us here.