set of various basalt rocks on white

background basalt black brown collage collection cut cutout extrusive gem gemstone geological glasbasalt glass glassbasalt glassy gray hyalobasalt igneous isolated macro mafic material mineral mineralogical natural out pebble piece polished porphyric porphyry raw rock rolled rough sample set specimen stone surface texture tholeiite tholeiitic tumbled unpolished various vitrobasalt white