A diamond, or rhombus is a four-sided shape, like a square turned on its side. All four sides of a rhombus are the same length but the angles on the corners do not have to be 90 degrees like in a square, the rhombus can be taller than it is wide or wider than it is tall. The window in the picture is diamond-shaped. A diamond is also a kind of precious stone.
Diamonds are made from carbon arranged in a very rigid crystalline pattern. This makes diamond the hardest substance in the world. It is also very good at dispersing light, which gives diamonds their sparkle. Diamonds are very popular in jewellery like rings and necklaces.