Igneous Rocks

Igneous – “FIRE ROCKS”

From red-hot magma…

Extrusive Igneous Rocksform when lava erupts

from a volcano or “bubbles up” from tectonic plates moving apart - onto Earth’s surface.

Ex: Basalt – the most common extrusive rock on Earth; forms most of Earth’s ocean floor.Ex: Obsidian – black volcanic glass

Igneous Rocks Earth's Most Abundant Bedrock: Basalt

Basalt forms more of Earth's surface than any other rock type. Most areas in ocean basins are basalt.

May be on land from lava flows, too.

Igneous Rock - Obsidian

Obsidian was used to make knives, arrow heads, spear points, scrapers and many other weapons and tools

How igneous rocks form…

ExtrusiveWhen a volcano erupts or when magma bubbles to the surface

Intrusive when magma cools slowly inside earth

Intrusive Igneous Rocks

forms when magma hardens beneath Earth’s surface (INSIDE).

Ex: Granite – the most abundant intrusive rock on Earth’s continents.Forms the core of many mountain ranges.

Ex: Porphyry- looks like jello w/fruit inside it

Intrusive Igneous Rocks

Granite is used to make many

objects

Granite is also well-known from its many world-famous natural exposures.

These include: Stone Mountain, GA; Mount Rushmore, SD

Intrusive Igneous Rock

Porphyry—mixed texture (some large and some small grains)

Igneous RocksTexture – fine grainedRapidly cooling lava forms a fine-grained

rock with small crystals.

Ex: Basalt - crystals too small to be seen without a microscope.

Ex: Obsidian –smooth, shiny texture like thick glass & cooled without forming crystals “Volcanic Glass”

Igneous Rocks

Obsidian

Obsidian on the side of a volcano

Igneous Rocks

Texture: coarse-grained

Slowly cooling magma forms coarse-grained rock with large crystals

• Ex: granite and porphyry

Igneous Rocks – Mineral Composition

Felsic: When magma is high in silica light-colored rocks form - like granite.

Mafic: When lava is low in

silica dark-colored rocks form - like basalt

High Silica vs. Low Silica

Felsic vs. Mafic

Uses of Igneous Rock

Granite – Statues, Bridges and old public buildings, Paving streets with cobblestone, floors, kitchen countertops (thin polished sheets of Granite)

Uses of Igneous RockBasalt - Gravel for construction

Obsidian - Sharp tools for cutting and scraping (Native Am!), Starting vegetable gardens (fertilizer) – it’s called Perlite, which is formed from heating Obsidian

Pumice is cool! It can float!

Pumice – used for cleaning and polishing

Uses of Igneous Rock

Statues, Public Buildings - Granite

Uses of Igneous Rocks

Cobblestone streets, kitchen countertops – Granite