1. Most are volcanic and extrusive in nature, rather than tectonic. 2. Andesite can be considered as the extrusive equivalent of plutonic diorite. 3. Granodiorite is felsic to intrusive igneous equivalent of the extrusive igneous dacite. 4. The ridges may be volcanotectonic features, composed of extrusives along fissures. 5. This extrusive igneous rock is known from only two geological formations worldwide. 6. The extrusive igneous rock equivalent of granite is rhyolite. 7. Generally speaking, phaneritic implies an intrusive origin; aphanitic an extrusive one. 8. Examples of extrusive rocks include basalt, rhyolite, andesite, obsidian and pumice. 9. Phonolite is the fine-grained extrusive equivalent. 10. Unlike the Sacramento Mountains, the neighboring Sierra Blanca is an extrusive igneous complex.
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