Metamorphic Rocks

Overview of Metamorphic Rocks

• Metamorphic rocks are rocks which have undergone a change in form due to the effects of heat and pressure, or through chemical activity.
• The origination of these rocks involves the existing rock substance, or protolith, being altered and restructured within the earth’s crust.
• These rocks contribute significantly to the geological record, providing valuable insight about events and conditions in the earth’s past.

Formation of Metamorphic Rocks

• The formation of metamorphic rocks involves a process referred to as metamorphism.
• This process commences due to changes in conditions within the earth’s crust, primarily involving temperature, pressure, or both.
• Metamorphism causes the protolith to chemically react and restructure over a timescale of thousands to millions of years.
• The process can be driven by tectonic forces or by the presence of a heat source such as magma.

Types of Metamorphism

• Metamorphism is classified into two broad types: regional metamorphism and contact metamorphism.
• Regional metamorphism occurs over large areas due to intense pressure and high temperature that significantly alters the rock structure.
• Contact metamorphism occurs when rocks are heated by contact with magma or lava, such as near volcanic activity.

Types of Metamorphic Rocks

• Metamorphic rocks can be broadly grouped into two categories: foliated and non-foliated.
• Foliated metamorphic rocks, such as slate and gneiss, display layers or bands of minerals due to the effects of pressure during their formation.
• Non-foliated metamorphic rocks, like marble and quartzite, do not have a layered or banded appearance and are often composed mostly of a single mineral.

Features of Metamorphic Rocks

• Certain features are characteristically associated with metamorphic rocks.
• Metamorphic foliations, like slaty cleavage and lineation, denote the orientations of minerals in the rocks due to deformation.
• Mineral assemblages in metamorphic rocks are reflective of the specific conditions of pressure and temperature that existed during their formation.

Role in the Rock Cycle

• Metamorphic rocks play a vital role in the rock cycle.
• They can be weathered and eroded to form sediments, which can subsequently form sedimentary rocks, or alternatively, they can recrystallise due to changes in environmental conditions to form new metamorphic rocks.

Importance of Metamorphic Rocks

• Metamorphic rocks hold considerable economic importance.
• They provide valuable resources such as precious gems (ruby, sapphire), metallic ores, building materials (marble, slate), and are a source of talc and graphite.

Thoroughly review how metamorphic rocks form, types of metamorphism, classification of metamorphic rocks, their features, role in the rock cycle, and economic significance.