Igneous rocks composed of at least 50% olivine are typically classified as ultramafic rocks.

Here are some common examples:

* Dunite: Almost entirely composed of olivine (over 90%)

* Peridotite: A mixture of olivine and other minerals like pyroxene, but olivine is the dominant mineral.

It's important to remember that the exact mineral composition can vary within these rock types. However, the defining characteristic of ultramafic rocks is their high olivine content, typically greater than 50%.