The rocks which created Nea and Palea Kameni are all lavas of the same type, the minor differences among them being of form rather than composition. All the lavas of these islands belong to the group which geologists call dacites: a volcanic rock whose chemical composition consists of 65-67% silica (SiO~) and 13-15% alumina, with other elements (principally iron, sodium, calcium, potassium and magnesium) in small quantities (2-5%). These elements are found in both the amorphous volcanic glass. and the mineral crystals which, together with the glass, make up these rocks. The principal minerals found in the Kameni dacites are: feldspars: silica-aluminum minerals with white, transparent crystais, - pyroxenes: silica-calcium-iron-magnesium minerals, with crystals varying from dark green to black, and olivines: magnesium-iron-silica minerals, with transparent honey- coloured or dark-green crystals.


The main differences in the appearance of the various lavas are ones of colour, which are due to different cooling rates. The dark-coloured, more fragmented lavas, like most of those forming Nea Kameni, underwent very rapid cooling, with the result that they contain a high percentage of volcanic glass. Slower cooling permits the formation of many minerals, giving the lava a light ashen colour and a more granular texture. Most of the lavas forming Palea Kameni are of this type. Both laboratory studies of the Kameni rocks and all the physicai and chemical parameters measured in the area tend to indicate that the magma which feeds the Kameni volcanic centers is located at a depth of two to four kilometres beneath the islands at a temperature of 950-1000 degrees centigrade, where it is concentrated in small pockets (magma chambers) which in turn are fed with molten rock from deeper layers.

The Volcano of Santorini