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What is an igneous rock?
Is a type of rock that forms when melted rock cools and solidifies. (fresh & new rocks)
How are igneous rocks formed?
Forms from the solidification of melt. Melt is classified as magma when it is underground and lave when it erupts onto the surface.
Magma
melts underground
Lava
melt erupted onto the surface
Intrusive
Cooling & crystallization of magma underground (plutonic)
Extrusive
Cooling & crystallization of melt materials at the surface (volcanic)
How are igneous rocks described?
We mainly focus on minerals composition and texture.
Composition= what minerals they’re made of
Texture= glassy, fine-grained, coarse-grained, or bubbly (vesicular)
How are igneous rocks classified?
By their composition/silica content (SiO2)
Percentage of Ultramafic
Less than 45% of silica (rich in Fe & Mg)
They look green/jet black
Percentage in Mafic
45-55% silica (Fe & Mg rich, dark color) EX: Basalts & gabbros
Percentage in Intermediate
55-65% silica (dark ferromagnesian & light si-rich)
Percentage in Felsic
More than 65% silica (lighter in color)