Octahedral crystal model, late 18th-early 19th century.
© Science Museum / Science & Society Picture Library
This wooden model is part of the Wollaston Collection from King's College, London. Wooden models such as this were used by Abbe Rene Just Hauy (1743-1822), a French mineralogist, to explain how crystal forms arise. The cube-shaped units are arranged in square layers, each one larger than the previous one, by an extra 'border' of cubes. Abbe Hauy was one of the first to show that crystal shapes fall into six geometrical groups. He suggested how they could be built up by stacking identical units in regular patterns.