Children recognise rocks by their weight, hardness, colour and jaggedness. They tend to apply the word ‘rock’ intuitively and often to mineral samples. 1 2 To the children studied, rocks had to be large, heavy and jagged. Smaller fragments were described as stones. Rock was at fi rst regarded as being made of only one substance, with consequent diffi culty in recognising granite as rock. Children were also confused when deciding whether a sample was natural or not, 1 3 house brick being regarded as rock because it contains some natural material. The opposite view was also taken: that a cut and polished piece of marble is not a rock and is not natural because to be natural it must be ‘untouched by mankind’. Children may classify rock specimens as ‘crystal rocks’ and ‘normal rocks’ and the word ‘crystal’ is used to describe both rock and mineral specimens, but only if the sample is thought to be attractive in appearance.