Gea y la formación de las rocas 3/3

Metamorphic and Igneous Rocks: Formation and Characteristics

Understanding Metamorphism

• The concept of schistosity is dismissed; the rock does not split into slabs. Neices form at high temperatures, growing minerals that are not planar, which affects their breakage patterns compared to slates and schists.

• Near the ruins of Mirabel Castle in Cáceres, contact metamorphism leads to the formation of rocks known as corneanas, similar to slates but with distinct characteristics that can be identified by breaking them.

• A mineral shaped like a cross indicates contact metamorphism; original slate heated by nearby magma formed these distinctive features, showcasing different types of metamorphic rocks.

Types of Igneous Rocks

• Magmas solidify or crystallize to form igneous rocks; their chemical composition and cooling rate determine final rock characteristics such as grain size and color.

• Two main groups of igneous rocks exist: plutonic (formed underground) and volcanic (formed on the surface). Plutonic rocks like granite form from slowly cooled magma within the Earth's crust.

Formation Processes

• Plutonic rocks arise when subducting lithospheric plates melt at certain temperatures, generating magma that incorporates continental material during its ascent.

• Volcanic rocks form when magma rises quickly due to fluidity or favorable pathways, reaching the surface as lava flows that cool rapidly into basalt.

Characteristics of Granitic Rock

• In Madrid's regional park, granites—abundant plutonic igneous rocks—exhibit a rough texture with visible grains representing different minerals formed during slow cooling.

• Granite consists mainly of quartz, feldspar, and mica; it fractures differently than metamorphic rocks due to its homogeneous structure.

Volcanic Landscapes

• The Canary Islands' landscape results from volcanic activity; Timanfaya National Park showcases basalt formations created from past eruptions resembling a lunar environment.

• Basalt appears black due to iron content; its fine-grained structure results from rapid cooling during lava flow. Gas bubbles create small voids in the rock.

Lava Flow Dynamics

• Thick lava forms corded shapes as it cools while flowing down volcano slopes. The orientation of these cords is perpendicular to magma movement direction.

• Caves in basalt occur when outer layers cool while inner lava remains hot and continues flowing until depletion leaves behind tunnels.