Tetrahedron Building Blocks

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A seven-piece puzzle assembles into three sizes of tetrahedron. The basic piece is made up of five rhombic dodecahedra and comes in two mirror-image versions, orange and yellow, shown in the photos. This piece is known as the "tetrahedron building block" or TBB. Solving the puzzle starts with ease: assemble a small tetrahedron (order 3) using one orange and one yellow TBB. The next step up is moderate difficulty: build a medium tetrahedron (order 4) using two orange and two yellow TBBs. The most challenging task requires three orange and three yellow TBBs, plus the red piece, to assemble a large tetrahedron (order 5). Every puzzle has only one solution. The unique shapes of the pieces take some time getting used to, but after playing with them for a while, the three challenges will probably seem easy. The base plate is optional and can help learners understand how the pieces fit together. A particularly demanding challenge is building "the Great Pyramid" by assembling 12 yellow pieces and 12 orange pieces into a tetrahedron of order 8. This puzzle has only one solution, but it's likely too difficult to solve by hand. It's interesting to note that tetrahedra of orders 6 and 7 cannot be built from TBBs because the number of rhombic dodecahedra is not a multiple of five. It remains unknown whether any tetrahedron above order 8 can be formed solely using TBBs.