Common Minerals of Igneous and Metamorphic Rocks | Geology Optional Notes for UPSC PDF Download

Common Minerals

Metamorphic Ore Minerals

Metamorphic ore minerals are formed during metamorphism, which is the process of altering pre-existing rocks due to changes in temperature, pressure, and/or fluid composition. These minerals can develop in various types of rocks, including sedimentary, igneous, and other metamorphic rocks.

Examples of Metamorphic Ore Minerals:

• 1. Staurolite: - Staurolite is a common metamorphic mineral that typically forms during medium to high-grade metamorphism. It often occurs in schist and gneiss and is recognized by its characteristic cross-shaped twinning.
• 2. Garnet: - Garnet is another prevalent metamorphic mineral found in a range of rock types. It comes in various colors and is often used as a gemstone. Garnets are indicators of metamorphic conditions and can provide insights into the rock's history.
• 3. Kyanite: - Kyanite is a blue silicate mineral that forms under high-pressure conditions. It is commonly found in schist and gneiss and is valued for its industrial applications, such as in the production of ceramics.
• 4. Sillimanite: - Sillimanite is a metamorphic mineral that occurs in medium to high-grade metamorphic rocks like schist and gneiss. It has distinct fibrous crystals and is known for its heat-resistant properties, making it valuable in certain industries.

Garnet

• Garnet is a commonly occurring metamorphic mineral that can develop under various geological conditions.
• It is frequently found in metamorphic rocks like schists and gneisses.
• Garnet may contain valuable ore minerals like gold, silver, and copper either as inclusions or replacements within its structure.

Staurolite

• Staurolite is another metamorphic mineral that typically forms in medium to high-grade metamorphic rocks such as schists and gneisses.
• It frequently includes other minerals like graphite, sulfides, and magnetite as inclusions.

Kyanite and Sillimanite: A Comparative Study

• Kyanite

  • Description: Kyanite is a mineral that forms under high-pressure metamorphic conditions, originating from the metamorphism of clay-rich sediments and pelitic rocks.
  • Inclusions: It can contain valuable ore minerals like corundum and rutile within its structure.
  • Example: When kyanite undergoes metamorphism, it can incorporate corundum, a precious gemstone, and rutile, a mineral used in various industrial applications.

• Sillimanite

  • Description: Sillimanite is a metamorphic mineral that typically forms at high temperatures and pressures, particularly in regional metamorphic environments.
  • Inclusions: It may contain valuable ore minerals such as corundum, tourmaline, and garnet.
  • Example: In regions experiencing intense metamorphism, sillimanite can incorporate corundum, tourmaline, and garnet, enhancing its mineral composition.

Metamorphic Ore Minerals

• Graphite

  Graphite is a type of metamorphic mineral that develops during the metamorphism of organic-rich sedimentary rocks like coal and shale.

  It holds significant importance as a source of graphite, which finds applications in items such as pencils, lubricants, and batteries.

  For instance, graphite in pencils provides a smooth writing experience due to its slippery nature on paper.

• Talc

  Talc represents another metamorphic mineral that emerges from the metamorphism of magnesium-rich rocks like serpentinite and dolomite.

  It serves as a crucial source of talc, which is utilized in a variety of industrial applications, including ceramics, paint, and cosmetics.

  For example, talc is a common ingredient in cosmetics such as baby powder due to its softness and ability to absorb moisture.

• Marble

  Marble, a metamorphic rock, originates from the metamorphism of limestone or dolomite.

  It may contain valuable ore minerals like magnesite, which is vital in the manufacturing of magnesium metal.

  Marble is often used in sculptures and architecture due to its beauty and ability to be polished to a smooth finish.

• Metamorphic Ore Minerals Overview

  These examples highlight the diversity of metamorphic ore minerals and their economic significance, influenced by factors such as specific mineral composition, metamorphic conditions, and geological context.

  Each mineral undergoes a unique transformation during metamorphism, leading to distinct properties and applications.

IGNEOUS ROCK MINERALOGY

Igneous rocks are formed from molten material (magma or lava) and are primarily composed of minerals. The mineral composition of igneous rocks is crucial in determining their properties, appearance, and classification.

Common Minerals in Igneous Rocks

• Quartz:
  • Quartz is frequently found in felsic rocks like granite and rhyolite. It consists of silicon and oxygen and often occurs as clear, glassy crystals.
• Feldspar:
  • Orthoclase Feldspar:
    • Common in felsic and intermediate rocks, imparting pink, reddish, or gray colors.
  • Plagioclase Feldspar:
    • More prevalent in intermediate to mafic rocks, displaying a range of colors due to varying compositions.
• Olivine:
  • Green mineral found in ultramafic rocks like peridotite and basalt, composed of magnesium, iron, and silica.
• Pyroxene:
  • Common in mafic and intermediate rocks, such as augite and hornblende, rich in iron and magnesium.
• Amphibole:
  • Darker minerals found in intermediate and some mafic rocks, often associated with water presence during magma formation.
• Biotite and Muscovite:
  • Biotite: Dark-colored mica in mafic rocks.
  • Muscovite: Light-colored mica in felsic rocks.
• Feldspathoids:
  • Minerals similar to feldspar but with less silica, found in alkali-rich igneous rocks like nepheline and leucite.
• Magnetite and Ilmenite:
  • Minerals serving as sources of iron and titanium in mafic and ultramafic rocks.

The combination and proportions of these minerals determine the overall mineral composition of an igneous rock. This, along with texture, aids geologists in classifying and understanding the rock's origin and history. Accessory minerals, present in smaller amounts, also offer insights into the rock's formation conditions.