Mafic

Intermediate

Felsic

- The mantle is made up of peridotite (ultramafic composition)

- So why/how do we end up with so many different magma compositions?

Textbook Figure 6.6a

Bowen’s Reaction Series

Obsidian (felsic)

-extrusive - cooled very quickly above surface

- “glassy” texture

Granite (felsic)

- intrusive – cooled slowly below surface

- “phaneritic” texture – mineral crystals are visible

Rhyolite (felsic)

- extrusive – cooled above surface

- “aphanitic” texture – mineral crystals are not visible to eye

IGNEOUS ROCK TEXTURES

Magma composition….

So what minerals are in a:

Felsic rock?Intermediate rock?Mafic rock?

Granite (felsic) – Intrusive – phaneritic texture

Rhyolite (felsic) – extrusive – aphanitic texture

Similar felsic composition, different cooling history

Diorite – intrusive – phaneritic texture

Andesite – extrusive – aphanitic texture

Similar intermediate composition, different cooling history

Gabbro – intrusive – phaneritic texture

Basalt – extrusive – aphanitic texture

Similar mafic composition, different cooling history

Page 177

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Textbook Figure 6.11a

Dike

Textbook Figure 6.11 b and c