GEOL 100 Igneous Rocks

Mode of Cooling: Intrusive

Texture: Phanateric

Mineral Composition: Felsic

Ex. Note: Has black/gray/white/pink dalmatian pattern 

Granite

Mode of Cooling: Extrusive

Texture: Aphanetic

Mineral Composition: Mafic

Basalt

Mode of Cooling: Intrusive

Texture: Phaneritic

Mineral Composition: Mafic

Gabbro

Mode of Cooling: Extrusive

Texture: Glassy

Mineral Composition: Felsic

Obsidian

Mode of Cooling: Extrusive

Texture: Aphanetic

Mineral Composition: Mafic

Ex Note: Has visible air bubbles aka Vesicular

Vesicular Basalt

Mode of Cooling: Intrusive

Texture: Phaneritic

Mineral Composition: Intermediate

Ex Note: Has black/white dalmatian pattern

Diorite

Mode of Cooling: Intrusive

Texture: Phaneritic

Mineral Composition: Ultramafic

Peridotite

Mode of Cooling: Extrusive

Texture: Vesicular

Mineral Composition: Mafic

Ex Note: Has visible air bubbles aka Vesicular

Scoria

Mode of Cooling: Extrusive

Texture: Vesicular

Mineral Composition: Felsic

Ex Note: Has visible air bubbles aka Vesicular

Pumice

Mode of Cooling: Extrusive

Texture: Aphanitic

Mineral Composition: Felsic

Rhyolite

Mode of Cooling: Extrusive

Texture: Aphanetic

Mineral Composition: Intermediate

Andesite

Mode of Cooling: Extrusive

Texture: Pyroclastic

Mineral Composition: Felsic

Rhyolitic Tuff

Mode of Cooling: Extrusive

Texture: Pyroclastic

Mineral Composition: Intermediate

Andesitic Tuff

Mode of Cooling: Extrusive

Texture: Pyroclastic

Mineral Composition: Mafic

Basaltic Tuff

Aphanitic 

A fine-grained rock composed of crystals of similar size that are too small to see with the naked eye. Aphanitic rocks that exhibit a small number of rounded cavities (vesicles) from gas bubbles have the term “vesicular” added to the name; e.g., vesicular basalt.

Phaneretic

Individual crystals are visible to the naked eye and are typically of roughly uniform size. Tends to form in large intrusive bodies, such as batholiths, stocks, laccoliths, dikes, and sills.

Vesicular

An aphanitic or glassy rock in which >30% of the total volume consists of roughly spherical, or partially rounded vesicles caused by gas bubbles that were trapped in the magma during rapid cooling

Pyroclastic

An assemblage of fragmental volcanic tephra (material ejected from a volcano). Can resemble a porphyritic texture in that larger particles are surrounded by fine-grained ones. However, the larger particles consist of ash, stones, shards, lapilli, and/or bombs that have been welded together rather than the single crystals found in porphyritic rocks. Most pyroclastic rocks contain angular open spaces (pores) between individual tephra particles.
The pores are typically microscopic, but can be >10 cm in size. Loose tephra can also be cemented by groundwater flow after it was deposited. Depending on the mineralogical composition, pyroclastic rocks may also contain chunks of pumice or scoria.

Felsic

Light-colored rocks that are mostly (>80%) composed of feldspar and silica, with at least 10% quartz content. In addition to being light colored, felsic rocks usually have a density similar to quartz, which is relatively light. The most common felsic rock is granite, which is intrusive; rhyolite is an extrusive rock that is chemically equivalent to granite.

Intermediate

Rocks with a grey, greenish, or salt and pepper coloration that contain 60-80% felsic minerals, but less than 10% quartz. The most common intermediate rock is andesite, which is extrusive; diorite is an intrusive rock that is chemically equivalent to andesite

Mafic

Dark-colored rocks that contain at least 40% magnesium and ferric minerals, where ferric means that the minerals contain iron. Quartz is not found in mafic rocks. In general, the presence of iron causes mafic rocks to be more dense than felsic rocks The most common
mafic rock is basalt, which is extrusive; gabbro is an intrusive rock that is chemically equivalent to basalt.

Ultramafic

Dark, dense rocks that are composed almost entirely (> 90%) of magnesium and ferric minerals. The most common ultramafic rock is peridotite; an intrusive rock that is thought to make up much of the oceanic crust, and upper mantle. The primary minerals in peridotite are olivine and members of the pyroxene family. Extrusive ultramafic rocks are extremely rare.