Ignis: means ignite in Latin.
Comes from magma in the mantle. Lava on the surface and magma in the mantle.
Classified by composition and texture.
Composition: means what minerals it is made from.
Texture: What are the shape, size, arrangement and distribution of the minerals?
Four basic textures:
Glassy - Shiny, no crystals: example-obsidian
Fine-grained very small crystals (need microscope to see): example - basalt
Coarse-grained mid-size crystals (visible to unaided eye): example - granite
Porphyritic Large crystals and small crystal (like rocky-road ice cream) example trachite
The way a rock forms influences its texture: The longer it takes to cool the larger the crystal size.
Extrusive Igneous rocks: form from lava When lava cools on or near the surface.
This produces very fine or no crystals (Glassy and Fine-grained texture)
Basalt and Obsidian are extrusive igneous rocks.
Pumice is formed at the very top of the surface and has many air bubbles because
it cooled so quickly.
Intrusive Igneous rocks: form from magma When magma cools deep within Earths surface.
Coarse-grained large crystals
Granite and many gemstone rocks are intrusive rocks.