Geo Gallery 3 : Basalt -- Varieties and Forms :

Basalt is an extrusive volcanic rock with a large array of different surface forms and hence belongs to the most interesting geological formations. Often basalt forms surprisingly regular columns, mostly six - sided (hexagonal) but also with 5 or 7 and more sides, which many people take for crystals. But these columns are no crystals at all, but regular cracks or joints formed by successive cooling of the lava along colder surfaces like other rocks or air slowly penetrating the basalt from surface to depth. Some impressive examples are shown here.

If the basaltic lava enters seawater or there is a submarine volcanic eruption, there will be no columns, but instead well-rounded basalt pillows will form. By tectonic uplifting these pillow lavas may be exposed on dry land and are a regular part of ophiolitic rock sequences, with good examples on Cyprus and in the Sultanate of Oman.

Please click (!) on the thumbnails to get a larger image with some description. If you have any questions, donīt hesitate to contact me.

Larger interactive panoramic images of Panska Skala and Hirtstein by Manuel Dahmann can be found here and here.