1. IGNEOUS ROCKS by Charina Cameron
Part 2: Textures

2. TEXTURES Aphanitic (finely crystalline) Porphyritic (phenocrysts)
Phaneritic (coarse)

3. TEXTURES
Cooling rates control crystal sizes

4. VOLCANIC GLASS
A glassy texture results from lava cooling very fast at Earth's surface
Obsidian
From a felsic magma
Black in thick pieces from traces of mafic minerals
Conchoidal fracture like window glass

5. INTRUSIVES - PHANERITIC TEXTURE
Felsic - granite
Intermediate - diorite
Mafic
Phaneritic - gabbro
Aphanitic - basalt

6. VOLCANICS - APHANITIC TEXTURE
Felsic - rhyolite
Intermediate - andesite
Mafic - basalt

7. PORPHYRITIC TEXTURES Phenocrysts = isolated crystals in a finer matrix
Rhyolite porphyry
Andesite porphyry
Basalt porphyry

8. PYROCLASTICS Ash (very fine, like flour) Lapilli (sandy to pebbly)
Bombs (cobble -like & larger)
Volcanic ash
Mount St. Helens (1980)

9. PYROCLASTICS Volcanic ash Lahars very fine-grained
can cover everything
Lahars
rain soaks ash
mudflows

10. CONSOLIDATED PYROCLASTICS
Tuff
Consolidated volcanic ash
Welded tuff = hot ashfused
Banded tuff (with glass)

11. EVIDENCE OF VOLCANIC GAS
Pumice
Vesicles in lava
Felsic magma
Scoria
Vesicles in basalt
Mafic magma
Hawaii
Amygdaloidal basalt
Vesicles filled with zeolite minerals
Larger & elongated vesicles near top of flow