Basalt

Basalt is lava cooled at the surface of the earth or in volcanic pipes that existed in the Western Sudeten Mountains 20-30 million years ago. This type of rock consists of tiny mineral crystals that can hardly be seen with the naked eye. Most of them are dark, so the rock is also dark, almost black. There are also sparse, round or oval, bottle-green olivine crystals called olivine bombs. As they get weathered, they turn into yellow sand. Basalt lava cooled down and cracked into more or less regular columns. Air and water make basalt weather, which makes fissures lighter, greyish, sometimes red-brownish, with mineral booms. You can see that in numerous scratches made while transporting this piece of rock from a mine near Lubań (Pogórze Izerskie).