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IGNEOUS ROCK CLASSIFICATIONS
   The list below are the identifications for the study tray of igneous rocks in the lab. If you have problems with any of the specimens see me or one of the assistants; some of the descriptions may not be completely accurate, so if what you get does not agree with this key let Fichter know. I will make my own analysis and change this key as necessary.
   Also, the header at the top of this page links to the igneous rock web site where you can look up descriptions/images of specific rocks, the eight rock forming minerals. etc.

1. Anorthosite: nearly 100% plagioclase
2. Andesite Porphyry: phenocrysts of Na plagioclase
3. Diorite: 60% plagioclase, 25% amphibole, 13% biotite, 2% qtz
4. Scoria
5. Rhyolite: 80% orthoclase, 18% biotite + qtz, 2% (trace amounts) of plagioclase
6. GranoDiorite: 65% qtz (pink and white), 20% biotite, 15% plagioclase
7. Vesicular Basalt
8. Basalt: 50% pyroxene, 40% Ca palgioclase, 10% olivine
9. GranoDiorite: 45% qtz, 20% biotite, 20% amphibole, 15% Na plagioclase
10. Gabbro: 70% pyroxene (blocky), 20% Ca plagioclase (iridescent), 10% qtz + biotite + Na plagioclase
11. GranoDiorite: 50% qtz, 20% Na plagioclase, 20% biotite, 10% amphibole
12. GranoDiorite: 45% qtz, 25% biotite, 20% plagioclase, 10% amphibole
13. AlkaliGranite: 50% orthoclase, 25% qtz, 16% plagioclase, 9% mafics
14. GranoDiorite: 45% qtz, 25% biotite, 20% plagioclase, 10% amphibole
15. Andesite Porphyry: 70% groundmass (aphanitic; too fined grained to see crystals), 25% phenocrysts of amphibole, some blocky, others elongate crystals.
16. AlkaliGranite
17. GranoDiorite: 65% multicolored qtz, 15% biotite, 15% muscovite, 5% plagioclase
18. Quartz Diorite: 40% amphibole, 35% biotite, 15% qtz, 10% Na plagioclase
19. Rhyolite Porphyry: 35% orthoclase, 30% qtz, 15% orthoclase phenocrysts, 10% plagioclase, 10% amphibole
20. Scoria
21. Diorite: 45% amphibole, 40% Na plagioclase, 10% biotite, 5% Ca plagioclase
22. Felsite Porphyry: 40% orthoclase, 25% qtz, 25% Na plagioclase, 10% phenocrysts of smoky qtz, biotite, amphibole, and pyroxene
23. PlagioGranite: 70% qtz, 20% Na plagioclase (iridescent), 10% amphibole + trace amounts of biotite
24. Dunite: 90% olivine, 10% amphibole + biotite + pyroxene
25. Gabbro: 40% Ca plagioclase, 20% Na plagioclase, 20% olivine, 20% pyroxene + biotite
26. Anorthosite: 95% plagioclase, 5% pyroxene + biotite
27. Gabbro: 60% plagioclase, 20% pyroxene, 15% amphibole, 5% olivine
28. Rhyolitic Tuft
29. GranoDiorite: 50% qtz, 20% plagioclase, 15% biotite, 15% amphibole
30. Gabbro: 55% plagioclase, 40% olivine, 10% pyroxene, 5% qtz
31. PlagioGranite: 45% qtz, 45% Na plagioclase, 10% amphibole + biotite
32. GranoDiorite: 70% qtz, 15% biotite, 15% Na plagioclase
33. GranoDiorite: 50% qtz, 30% Na plagioclase, 20% amphibole + biotite
34. Pumice
35. Andesite Porphyry: 70% groundmass (aphanitic; too fined grained to see crystals), 25% phenocrysts of amphibole, some blocky, others elongate crystals.
36. Rhyolitic Porphyry

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Last Update: 01/05/01

e-mail: (Fichtels@jmu.edu)