Differentiation Index

The Differentiation Index: A Measure of Rock Differentiation

Introduction

The differentiation index is a measure of the degree of differentiation a rock has undergone. It was defined in 1960 by two American petrologists, C. Tuttle and O.F. Tuttle. The differentiation index is calculated using a series of equations that involve the concentrations of various elements in the rock.

The Differentiation Index Formula

The differentiation index is calculated using the following formula: ``` DI = (Si + K)/100 ``` where: * DI is the differentiation index * Si is the weight percentage of SiO2 in the rock * K is the weight percentage of K2O in the rock

Interpretation of the Differentiation Index

The differentiation index can be used to classify rocks into three different types: * **Undifferentiated rocks:** DI < 50 * **Moderately differentiated rocks:** 50 ≤ DI < 75 * **Highly differentiated rocks:** DI ≥ 75 Undifferentiated rocks are those that have not undergone much differentiation. They are typically composed of a mixture of minerals that are similar in composition. Moderately differentiated rocks have undergone some differentiation, but they still contain a mixture of minerals that are different in composition. Highly differentiated rocks have undergone a great deal of differentiation, and they are typically composed of minerals that are very different in composition.

Applications of the Differentiation Index

The differentiation index is used in a variety of applications, including: * **Petrogenesis:** The differentiation index can be used to determine the origin of a rock. Rocks that have a high differentiation index are typically formed from magmas that have undergone a great deal of differentiation. * **Mineral exploration:** The differentiation index can be used to explore for mineral deposits. Rocks that have a high differentiation index are more likely to contain valuable minerals. * **Environmental geochemistry:** The differentiation index can be used to assess the environmental impact of rocks. Rocks that have a high differentiation index are more likely to release harmful elements into the environment.

Conclusion

The differentiation index is a valuable tool for understanding the composition and origin of rocks. It can be used in a variety of applications, including petrogenesis, mineral exploration, and environmental geochemistry.