What is the Difference Between Dike and Sill?

Dikes and sills are both types of igneous intrusions, but they differ in their orientation and relationship with the surrounding rock layers. Here are the main differences between them:

1. Orientation: Dikes are formed when magma enters a rock fault and crystallizes, cutting vertically through rock layers. In contrast, sills are formed when magma intrudes horizontally between rock layers.
2. Crosscutting: Dikes are discordant intrusions, meaning they cut across preexisting rocks. Sills, on the other hand, are concordant intrusions, meaning they do not cut across preexisting rocks but rather intrude parallel to the original rock or landform.
3. Emplacement: Sills are often fed by dikes, except in unusual locations where they form in nearly vertical beds attached directly to a magma source.

In summary, dikes and sills are both igneous intrusions, but they differ in their orientation and relationship with the surrounding rock layers. Dikes are vertical intrusions that cut across preexisting rocks, while sills are horizontal intrusions that do not cut across preexisting rocks and are often fed by dikes.

Comparative Table: Dike vs Sill

Here is a table comparing the differences between dikes and sills:

Dikes are sheets of rock that form in fractures within pre-existing rock bodies. They can be either magmatic or sedimentary in origin, with magmatic dikes forming when magma intrudes into a crack and then crystallizes as a sheet intrusion. Sills, on the other hand, are tabular sheet intrusions that have intruded between older rock layers, forming a concordant intrusive sheet. Magmatic sills form from magma that intrudes between rock layers, while sedimentary sills form when sediment fills a pre-existing crack.