Extrusive igneous rocks are formed when magma erupts onto the Earth's surface as lava and cools quickly. This rapid cooling doesn't give the crystals much time to grow, resulting in small, fine-grained crystals, often referred to as phaneritic.

Here are some examples of crystals commonly found in extrusive igneous rocks:

* Feldspar: A common mineral found in many igneous rocks, feldspar can be found in various forms, including plagioclase and orthoclase.

* Quartz: Another common mineral, quartz is known for its hardness and glassy appearance.

* Pyroxene: A group of silicate minerals with a characteristic prism shape.

* Amphibole: A group of silicate minerals similar to pyroxene, but with a more complex chemical composition.

* Olivine: A green mineral found in mafic and ultramafic rocks.

It's important to note that not all extrusive igneous rocks have visible crystals. Rocks with a very fine-grained texture, known as aphanitic, might appear glassy or have a very fine, powdery appearance.

Overall, the type of crystals found in extrusive igneous rocks depends on the composition of the magma and the cooling rate.