Interlocking blocks

The invention provides an apparatus to form a 2 or 3 dimensional array of blocks. Each block has a cross-section of a plurality of sides with a tongue-groove pair per side, such that the tongue-groove pair is adjacent to each other and in the middle of each side. Each block has a cylindrical section protruding up from the center of the top of the block and a cylindrical section protruding in the center of the bottom of the block. Each block can be connected to other blocks to form a 2-dimensional array of blocks and to at most 2 other blocks to form a 3-dimensional array of blocks. The other blocks can be connected to a block to form a right angled 2-dimensional array or a skewed 2-dimensional array. Each block is transparent, translucent in various degrees, or opaque.