1. Textures & classification
aka “name-calling”

2. Updates Today’s topics: Classification of igneous rocks Textures
3rd lab = Field trip

5. Volcanic rocks: aphanitic

6. Ultra-mafic rocks & felsic vs. mafic

7. Classification of Igneous Rocks
Figure 2-2. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.
Olivine
Clinopyroxene
Orthopyroxene
Lherzolite
Harzburgite
Wehrlite
Websterite
Orthopyroxenite
Clinopyroxenite
Olivine Websterite
Peridotites
Pyroxenites 90 40 10
Dunite
(c)

8. Classification of Igneous Rocks
Figure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, Oxford University Press.

9. Classification of Igneous Rocks
Ash (< 2 mm)
Lapilli (2-64 mm)
Lapilli-
Tuff
Lapilli
stone
Tuff 30 30
Lapilli -
Tuff
Breccia 70 70
Pyroclastic
Breccia or
Agglomerate
Blocks and Bombs
(> 64 mm)
(b)
Figure 2-5. Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1,

10. Textures: result of nucleation+growth

11. Grain size

12. Fast growth a
Ocean Drilling Program

13. Crystal zoning

14. Crystal shape

15. Growth order

16. Quartz - feldspar intergrowth

17. Remelting

18. Matrix texture

19. Twinning

20. Replacements
North Carolina
State University
Smith College