Igneous extrusive layer

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Created when magma exits a volcano and cools above the Earth's surface.

Igneous extrusive stone layers are formed from andesite, basalt, dacite, obsidian, and rhyolite. Of these five, andesite, dacite, and rhyolite are functionally identical, different only in appearance and name, basalt is like the other three except that it is magma-safe, and obsidian is... unique.

Igneous extrusive layers

• Rhyolite
• Basalt
• Andesite
• Dacite
• Obsidian

Stone found in igneous extrusive layers

• Hematite (veins)
• Native copper (veins)
• Galena (veins)
• Cinnabar (veins)
• Brimstone (small clusters)
• Realgar (small clusters)
• Orpiment (small clusters)
• Stibnite (small clusters)
• Magnetite (small clusters)
• Native aluminum (small clusters)
• Alunite (large clusters)

Stone appearing in both igneous intrusive and igneous extrusive layers

• Native gold (veins)
• Cobaltite (veins)
• Pyrolusite (small clusters)
• Hornblende (small clusters)

Gems found in igneous extrusive layers

• Turquoise (small clusters)

Gems appearing in both igneous intrusive and igneous extrusive layers

• Black zircon (small clusters)
• Green zircon (small clusters)
• Red zircon (small clusters)
• Brown zircon (small clusters)
• Yellow zircon (small clusters)
• Clear zircon (small clusters)

* See also: stone found everywhere

In Real Life

In real-world geology, Igneous extrusive stone is formed by lava solidifying above the surface, open to the air. This is the main point of difference from igneous intrusive stone, which solidifies below the surface. This distinction is not kept in Dwarf Fortress geology, in which the difference is simply the name and contents of the two types of stone.

V · T · E Stones
Sedimentary	Calcite · Chalk · Chert · Claystone · Conglomerate · Dolomite · Limestone · Mudstone · Rock salt · Sandstone · Shale · Siltstone
Igneous	Intrusive Diorite · Gabbro · Granite Extrusive Andesite · Basalt · Dacite · Obsidian · Rhyolite
Metamorphic	Gneiss · Marble  · Phyllite · Quartzite · Schist · Slate
Ore	Adamantine, raw · Aluminum, native · Bismuthinite · Cassiterite · Copper, native · Galena · Garnierite · Gold, native · Hematite · Horn silver · Limonite · Magnetite · Malachite · Platinum, native · Silver, native · Sphalerite · Tetrahedrite
Economic	Alabaster · Bituminous coal · Calcite · Gypsum · Kaolinite · Lignite · Satinspar · Selenite
Other	Alunite · Anhydrite · Bauxite · Borax · Brimstone · Chromite · Cinnabar · Cobaltite · Cryolite · Graphite · Hornblende · Ilmenite · Jet · Kimberlite · Marcasite · Mica · Microcline · Olivine · Orpiment · Orthoclase · Periclase · Petrified wood · Pitchblende · Puddingstone · Pyrolusite · Realgar · Rutile · Saltpeter · Serpentine · Slade · Stibnite · Sylvite · Talc