Just an addition. These things are not of the carved expanded polystyrion type but cast in moulds somehow. According to Peter it's a mixture of acrylics, a special plaster and celluose (it won't break and is tough but you can be cut it easily - the rock needles come in two parts each, so you have to make the top fit). They are hollow but sturdy, a bit flexible and very light concerning the weight. Unpainted and unflocked they have the same dark-grey colour as the the Ziterdes rock pieces.
JO