Phaneritic Texture - Environmental Geology - Lecture Slides, Slides of Earth Sciences

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Phaneritic Texture

Cooling Rate and Texture • Two stage history – Usually occurs with a slow phase first, then a fastphase as magma rises to the surface – Produces big crystals in a field of little crystals – Porphyritic Texture—Two distinctly different crystalsizes

Cooling Rate and Texture • Glass – Usually attributed to very rapid cooling – Not quite so simple – Material is not crystalline

Cooling Rate and Texture • Vesicular – Gas trapped as bubbles – Produces holes called^ vesicles – Vesicles filled with mineral material are amygdales • Fragmental – Made of chunks – Pyroclastic—chunks are dominantlyigneous material

Classification of Igneous Rocks Texture^ Felsic^ Intermediate

Mafic^ Ultramafic Phaneritic^ Granite^ Diorite

Gabbro^ Peridiotite,Dunite, etc. Aphanitic^ Rhyolite^ Andesite

Basalt^ Komatiite Porphyritic^ RhyoliteAndesiteporphyryporphyry

Basaltporphyry Glassy^

Obsidian Vesicular^ Pumice^

Vesicular Basalt Fragmental^ Tuff and Volcanic Breccia

Igneous Rocks

Where Does Magma Come From? • Something has to melt – Garnet peridotite of the mantle – Wet oceanic crust during subduction – Granitic to andesitic continental crust