11. Basalt is a dark colored extrusive volcanic rock. 12. It used to be found in fissure veins in the extrusive igneous rhyolite rock. 13. Some species have extrusive organelles ( trichocysts ). 14. Extrusive products include rhyolitic ignimbrites along with basalt, andesite, and rhyolite lava flows.15. Extrusive igneous rock are dominant above on the eastern slope and on the western slope.16. This is an extrusive igneous rock. 17. As might be expected, they show structures intermediate between those of extrusive and plutonic rocks. 18. Well-known examples of outcropping trap rock include both intrusive sills and extrusive lava flows. 19. Hughes Mountain is formed of extrusive rhyolite which joints when it cooled, creating polygonal columns. 20. Over large areas extrusive rocks lie in flat undisturbed piles on a Cenozoic surface of moderate relief.
