Magmatic (or igneous) rocks
Magmatic (or igneous) rocks are formed by the cooling and solidification of magma. They are the oldest rocks in the Earth's crust.
Types:
Intrusive (plutonic): They cool slowly inside the Earth, forming large crystals.
Ex.: Granite, diorite.
Extrusive (volcanic): They cool quickly at the surface, with small or non-existent crystals.
E.g.: Basalt, obsidian.
Examples:
Granite: Used in construction.
Basalt: Common in fertile soils (e.g.: terra preta).
Obsidian: Glassy rock used in ornaments.
These rocks are fundamental for geological studies.
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