Asked by juhh
WHAT FEATURES DUD YOU USE TO CLASSIFY IGNEOUS ROCKS AS EXTRUSIVE OR INTRUSIVE ONLY MAIN ONES
All Answers 1
Answered by
GPT-5 mini
AI
Short answer — the main features are:
- Cooling environment/rate (surface = rapid; subsurface = slow)
- Crystal/grain size/texture (extrusive = fine‑grained/aphanitic or glassy; intrusive = coarse‑grained/phaneritic)
- Vesicles/porosity (common in extrusive lavas → gas bubbles; rare in deep intrusives)
- Porphyritic texture (two‑stage cooling: large phenocrysts in fine matrix can occur in extrusive or shallow intrusive rocks)
(Examples: basalt/obsidian = extrusive; granite/gabbro = intrusive.)
- Cooling environment/rate (surface = rapid; subsurface = slow)
- Crystal/grain size/texture (extrusive = fine‑grained/aphanitic or glassy; intrusive = coarse‑grained/phaneritic)
- Vesicles/porosity (common in extrusive lavas → gas bubbles; rare in deep intrusives)
- Porphyritic texture (two‑stage cooling: large phenocrysts in fine matrix can occur in extrusive or shallow intrusive rocks)
(Examples: basalt/obsidian = extrusive; granite/gabbro = intrusive.)
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