What type of rock is a fine grained rock?
Fine grained rocks, where the individual grains are too small to see, are called aphanitic. Basalt is an example. The most common glassy rock is obsidian.
What is an example of a fine grained extrusive igneous rock?
Andesite is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene, and biotite.
What does fine grained mean in rocks?
i. Said of a crystalline rock, and of its texture, in which the individual minerals are relatively small; specif. said of an igneous rock whose particles have an average diameter less than 1 mm.
Why do extrusive igneous rocks have fine grained?
Extrusive Igneous Rocks: Quick cooling means that mineral crystals don’t have much time to grow, so these rocks have a very fine-grained or even glassy texture. Hot gas bubbles are often trapped in the quenched lava, forming a bubbly, vesicular texture.
Which of these rock types has a fine-grained texture?
Extrusive igneous rocks have a fine-grained or aphanitic texture, in which the grains are too small to see with the unaided eye. The fine-grained texture indicates the quickly cooling lava did not have time to grow large crystals. These tiny crystals can be viewed under a petrographic microscope [1].
What is a fine rock texture?
Fine-grained textures generally indicate magmas that rapidly cooled at or near the Earth’s surface. Fast cooling prevents crystals from growing very large. The cutoff between fine- and coarse-grained textures is about 1 mm. All four photos below are of the mafic rock basalt.
What are the examples of extrusive igneous rocks?
Types of extrusive igneous rocks include: pumice, obsidian, andesite, rhyolite, and basalt.
Which igneous rocks are fine grained?
Igneous Rocks by Composition
| Coarse-Grained Textures | Fine-Grained Textures |
|---|---|
| Peridotite = Ultramafic | Komatiite (Ultramafic, but too rare to worry about at this point in your life) |
| Gabbro = Mafic | Basalt = Mafic |
| Diorite = Intermediate | Andesite = Intermediate |
| Granite = Felsic | Rhyolite = Felsic |
How are fine grained rocks formed?
If magma cools quickly, for example when basalt lava erupts from a volcano, then many crystals form very quickly, and the resulting rock is fine-grained, with crystals usually less than 1mm in size. If magma is trapped underground in an igneous intrusion, it cools slowly because it is insulated by the surrounding rock.
How are fine-grained igneous rocks formed?
Fine-grained igneous rocks form when lava cools quickly at Earth’s surface. How do fine-grained igneous rocks form? mostly quartz and feldspar and thus are light-colored. Basaltic rocks are rich in iron and thus are dark-colored and more dense.
What characteristics do extrusive igneous rocks have?
Igneous rocks which form by the crystallization of magma at the surface of the Earth are called extrusive rocks. They are characterized by fine-grained textures because their rapid cooling at or near the surface did not provide enough time for large crystals to grow.