Almost 150 different species of minerals have been detected in Iceland. Their formation can come about in different ways, e.g. through the clotting of lava. Minerals can also be formed out of warm water seeping through rock, eventually transforming into concretions and crack- or fracture fillers. This is called low temperature alterations, taking place at 50° - 300° C over an extended period.
These fillings are made of ingredients which the warm water has dissolved from the rock itself or from nearby rock formations. Thus minerals materialize through new conditions coming about in the rock. Added heat and pressure cause the rock to transform. Amygdales are confined to certain area, mainly to be found in ancient rock formations in East-, North- and West- Iceland.
The majority of minerals can be classified as the so-called quartz-minerals and their terminology and classification is mostly based on their respective colours which are the result of mixing of various components, the quarz itself being a clear silica. The majority of quartz minerals develop as fillings in holes or crevasses in rock formations.
(Steindór Steindórsson of Hlaðir: „ The Ode of the Rock")