Igneous Rocks

* When magma or lava cools and freezes, it becomes a mineral. * A combination of minerals is a Rock. * Igneous rocks are formed from the crystallization of magma or lava. -“Ignis,” the Greek word for “fire,” is like “Ignite,” the English word for “to light”

How Are Igneous Rocks Classified?

1) By Texture a) Extrusive -cooled above ground (lava) cooled quickly (a small amount of time) small crystals (they cooled too quickly for large crystals to grow) may have a glassy texture (no crystals) Fine Grained

How Are Igneous Rocks Classified? 1) By Texture b) Intrusive cooled inside the Earth (magma) cooled off slowly (a big amount of time) large crystals (they had time for big crystals to grow) Coarse grained

How Are Igneous Rocks Classified? 1) By texture c) Porphyritic has big and small crystals slow cooling magma erupted and finished cooling off quickly

How Are Igneous Rocks Classified? 2) By Mineral Composition a) Felsic Light color Lightweight High amount of silica Examples: granite, rhyolite

How Are Igneous Rocks Classified? 2) By Mineral Composition b) Intermediate Medium color Medium weight Less silica Examples: andesite, diorite

How Are Igneous Rocks Classified? 2) By Mineral Composition c) Mafic Dark color Heavy Low silica content Rich in iron and magnesium Examples: basalt, gabbro

How Are Igneous Rocks Classified? 2) By Mineral Composition d) Ultramafic Very dark color Very heavy Little silica Rich in iron and magnesium Form deep underground Example: peridotite, kimberlite

Which of the igneous rocks pictured below contains the greatest amount of iron and magnesium? BasaltGranite or

DARK LIGHT

State the relative crystal size (fine, med., or coarse grained) for igneous rocks that cooled and solidified at locations A, B, and C. A. B. C.

A. B. C. Coarse Grained Fine Grained Medium Grained Where might a porphyritic texture form?

MineralPercentage Plagioclase Feldspar 58 % Amphibole31% Biotite11% State the name of the igneous rock that has a coarse grained texture and the following mineral composition:

Scrap Paper

58%

Scrap Paper 58%

Igneous Rocks Magma Classifications 1) Rhyolitic 70% Silica (SiO 2 ) 2) Andesitic 60% SiO 2 3) Basalitic 50% SiO 2 Basalt is what makes up the ocean crust. If only 50% is silica, there is room for heavier elements in basaltic magma.