Red diamonds, also known as "fancy red diamonds", are extremely rare and are not found in any specific rock type. They are found in the same types of rocks as other diamonds:

* Kimberlite: This is the most common type of rock where diamonds are found. It's a volcanic rock formed deep within the Earth's mantle.

* Lamproite: A rarer type of volcanic rock, but also known to contain diamonds.

However, the color of a diamond is not determined by the rock it's found in, but rather by the presence of trace elements during its formation. Red diamonds get their color from a specific type of defect in their crystal structure.

It's important to note that red diamonds are extremely rare, and finding one in any rock type is incredibly unlikely.