Metamorphic Rock Metamorphic Rock forms from existing rocks (igneous, sedimentary, or even older metamorphic rocks) altered by intense heat, pressure, or hot, mineral-rich fluids deep within the Earth. This transformative process, called metamorphism, doesn’t melt the rock but reshapes its mineral structure and texture, creating denser, more compact forms.
The Metamorphic Process: Change Under Pressure
Metamorphism occurs when rocks endure conditions found deep underground or where tectonic plates collide. High temperatures and pressures, along with chemically active fluids, trigger changes in the rock’s mineralogy and fabric. Existing minerals recrystallize into new, stable forms, or their components rearrange. This process can even transform previously metamorphosed rock metamorphic rock into a new type. The resulting metamorphic rocks often exhibit signs of stress, such as being squished, folded, or smeared. Importantly, the rock doesn’t melt; if it did, it would become igneous rock.
Classifying Metamorphic Rock Metamorphic Rock: Foliated vs. Non-foliated
Metamorphic rock metamorphic rock is broadly categorized into two groups based on texture: foliated and non-foliated. Foliated rocks display a layered or banded appearance due to the parallel alignment of mineral grains. This alignment results from intense pressure squeezing flat or elongated minerals into a planar arrangement. Examples include gneiss and schist, which exhibit distinct stripes or layers.
Non-foliated metamorphic rocks lack this layered structure. This can occur for several reasons. The original rock might consist of minerals that aren’t flat or elongated, preventing alignment even under pressure. Limestone, primarily composed of calcite, is a prime example. Another formation process, contact metamorphism, involves the “baking” of existing rock by intruding magma. The heat alters the mineral structure without the application of directional pressure, resulting in rocks like quartzite and marble.
Common Examples of Metamorphic Rock Metamorphic Rock
The variety of metamorphic rock metamorphic rock reflects the diverse conditions under which they form. Common examples include:
- Phyllite: A fine-grained, foliated rock with a sheen.
- Schist: A medium to coarse-grained, foliated rock often containing prominent mica crystals.
- Gneiss: A coarse-grained, foliated rock with alternating light and dark mineral bands.
- Quartzite: A hard, non-foliated rock formed from sandstone.
- Marble: A non-foliated rock formed from limestone or dolostone, often exhibiting a crystalline texture.
Metamorphic rock metamorphic rock provides valuable insights into the Earth’s dynamic processes and history. Its formation reveals the intense forces acting within the planet’s crust and the continuous cycle of rock transformation.
