Basalt and rhyolite both are extrusive igneous rock that contains mineral crystals. However, the mineral crystals are normally less than 1 mm in diameter, and are therefore not discernible without magnification.
instrusive Rock
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.
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.
Extrusive igneous rocks are formed from lava that cools and solidifies quickly on the Earth's surface. This rapid cooling results in small mineral crystals or a glassy texture in the rock. Examples of extrusive igneous rocks include basalt, andesite, and rhyolite.
Basalt is the most common extrusive igneous rock.
Intrusive rock normally has visible crystals. Extrusive igneous rock has small crystals. A black extrusive igneous rock with small crystals could be basalt.
granite
by the size of the crystals, big crystals intrusive, small crystals extrusive
small crystals
== Grain size. Most intrusive igneous rocks will have visible crystals. Crystals in most extrusive igneous rocks are not easily visible.
instrusive Rock
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.
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.
Volcanic glass is an extrusive igneous rock. It forms when molten lava cools quickly on the Earth's surface, preventing the formation of crystals.
An intrusive igneous rock has larger crystals than an extrusive igneous rock because it has had a longer period of time to solidify underground.
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.
A volcano is made of extrusive igneous rock. The specific type of igneous rock will vary from one volcano to another.