granite
Intrusive rock normally has visible crystals. Extrusive igneous rock has small crystals. A black extrusive igneous rock with small crystals could be basalt.
An intrusive igneous rock has larger crystals than an extrusive igneous rock because it has had a longer period of time to solidify underground.
Extrusive igneous rock consists of mineral crystals that are not observable with the naked eye. Obsidian is an extrusive igneous rock (volcanic glass) where there technically are no mineral crystals.
by the size of the crystals, big crystals intrusive, small crystals extrusive
If you're not looking for anything specific, any extrusive igneous rock will have smaller crystals, if any at all. This is because they cool quickly on the surface, leaving little time for crystals to form/grow.
Large crystals are typically characteristic of intrusive igneous rocks, which form beneath the Earth's surface from slow cooling of magma. Extrusive igneous rocks cool quickly at or near the Earth's surface, resulting in smaller crystals or glassy textures.
Igneous rocks can have both small and large crystals, depending on how quickly they cool. If an igneous rock cools slowly beneath the Earth's surface, it can form large crystals, while rapid cooling at the Earth's surface or in an eruption can result in small or no visible crystals.
small crystals
== Grain size. Most intrusive igneous rocks will have visible crystals. Crystals in most extrusive igneous rocks are not easily visible.
instrusive Rock
A volcano is made of extrusive igneous rock. The specific type of igneous rock will vary from one volcano to another.
You would expect to find an igneous rock with small crystals near the Earth's surface where the rock cools relatively quickly, such as in volcanic eruptions or magma intrusions that do not have much time to grow large crystals. These rocks are known as volcanic or extrusive igneous rocks.