set of various basalt stones cutout on white

background basalt black brown close closeup collage collection cut cutout extrusive gemstone geological geology glass glassbasalt glassy gray hyalobasalt igneous isolated mafic magmatic mineral mineralogical mineralogy natural obsidian out piece polished porous porphyrisch porphyritic raw rock rough sample set specimen stone tholeiite tholeiitic tholeite tumbled tumbling unpolished various vitrobasalt volcanic white