Decoding Granodiorite’s Puzzle: Unraveling the Superior Dispersion of CaO Over K2O

Why is CaO more finely distributed than K2O in granodiorite?

1. Introduction

Granodiorite is a common intrusive igneous rock composed primarily of quartz, plagioclase feldspar, and a minor amount of potassium feldspar. It belongs to the family of granitic rocks and is known for its coarse-grained texture. Granodiorite often exhibits variations in mineral composition, particularly in the distribution of calcium oxide (CaO) and potassium oxide (K2O). The purpose of this article is to explore the reasons for the finer distribution of CaO compared to K2O in granodiorite.

2. Mineralogical composition of granodiorite

Granodiorite is composed of several minerals, the most prominent being quartz, plagioclase feldspar and potassium feldspar. Plagioclase feldspar typically makes up the majority of the feldspar content of the rock and can be further divided into two types: oligoclase and andesine. Oligoclase contains a higher concentration of CaO, while andesine contains more sodium oxide (Na2O). Potassium feldspar contains a higher concentration of K2O.
When granodiorite undergoes the process of crystallization from a molten state, minerals form in a specific order based on their melting points. Quartz, which has a high melting point, crystallizes first, followed by plagioclase feldspar and then potassium feldspar. This sequential crystallization process results in the formation of distinct mineral grains within the rock.

3. Factors Affecting Mineral Distribution

Several factors influence the distribution of minerals within granodiorite, including the chemical composition of the magma, the cooling rate of the magma, and the presence of hydrothermal fluids. In the case of CaO and K2O, their distribution can be attributed to differences in their geochemical behavior during the crystallization process.

CaO is more likely to be finely dispersed in granodiorite due to its greater compatibility with the other minerals present. Compatibility refers to

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