Igneous extrusive layer
From DwarfFortressWiki
Igneous extrusive stone layers usually include Hematite, Gold, Copper, and Tetrahedrite.
Andesite, Basalt, Felsite, Obsidian, and Rhyolite layers are igneous extrusive.
Their name appears in a darker shade on the embark menu. They also indicate a good chance of magma being present in some form or another.
