Sample Solution

BGYCT-135 Solved Assignment 2024

Part A

1. Write short notes on the following: a) Extraterrestrial Rocks b) Phase Rule

Answer:

a) Extraterrestrial Rocks

Extraterrestrial rocks, also known as meteorites, are rocks that originate from celestial bodies such as asteroids, comets, and planets other than Earth. These rocks provide valuable insights into the formation and evolution of the solar system and have significant scientific and historical importance.

Meteorites are classified into three main types based on their composition: stony meteorites, iron meteorites, and stony-iron meteorites. Stony meteorites are the most common and are composed mainly of silicate minerals. Iron meteorites are primarily composed of iron-nickel alloys, while stony-iron meteorites contain a mix of silicate minerals and metal.

Meteorites can be further classified based on their texture and structure. For example, some meteorites exhibit a characteristic fusion crust, which forms when the meteorite melts as it passes through Earth's atmosphere. Others may contain chondrules, which are small, spherical grains that formed early in the solar system's history.

Studying meteorites provides valuable information about the early solar system. For example, the presence of certain isotopes in meteorites has been used to determine the age of the solar system. Meteorites also contain primitive materials that have remained relatively unchanged since the formation of the solar system, providing clues about the processes that occurred during this time.

Meteorites can also provide insights into the geology of other planets and celestial bodies. For example, some meteorites are believed to have originated from Mars, and studying them has helped scientists learn more about the geology and history of the red planet.

In addition to their scientific value, meteorites also have cultural and historical significance. They have been revered by many cultures throughout history and have been used in jewelry, tools, and religious artifacts.

In conclusion, extraterrestrial rocks, or meteorites, are valuable sources of information about the formation and evolution of the solar system. They provide insights into the geology of other planets and celestial bodies and have cultural and historical significance. Studying meteorites continues to advance our understanding of the universe and our place within it.

b) Phase Rule

Phase Rule in Petrology

The Phase Rule, formulated by Josiah Willard Gibbs in 1876, is a fundamental principle in petrology, the study of rocks and their formation. It provides a quantitative framework for understanding the equilibrium relationships between different phases in a heterogeneous system. In the context of petrology, these phases can be minerals, melts, or fluids present in a rock.

The Phase Rule is expressed as: F = C – P + 2

Where:

• F is the number of degrees of freedom or variance, representing the number of independent variables (such as temperature, pressure, or composition) that can be altered without changing the number of phases in equilibrium.
• C is the number of components, which are the chemically independent constituents needed to describe the composition of all phases in the system.
• P is the number of phases, which are the physically and chemically distinct parts of the system.

In petrology, the Phase Rule helps to understand the conditions under which different mineral assemblages can coexist in equilibrium. For example, in a simple system with one component (C=1), such as the silica (SiO2) system, the Phase Rule can be used to predict the stability fields of different polymorphs of silica (quartz, tridymite, and cristobalite) as a function of temperature and pressure.

The Phase Rule also has important implications for the study of metamorphic rocks, where it helps to decipher the P-T conditions (pressure-temperature) under which the rocks formed. By analyzing the mineral assemblages present in a metamorphic rock, petrologists can use the Phase Rule to constrain the metamorphic conditions and understand the geological processes involved in the rock's formation.

In igneous petrology, the Phase Rule is applied to understand the crystallization sequence of minerals from a melt and the evolution of magma composition. It helps to predict the order in which minerals crystallize as magma cools and solidifies.

Overall, the Phase Rule is a powerful tool in petrology, providing a theoretical framework for understanding the stability and coexistence of different mineral phases in the Earth's crust and mantle under varying conditions of temperature, pressure, and composition.