Rocks Rocks and More Rocks Igneous FIRE ROCKS

Rocks, Rocks and More Rocks! Igneous – “FIRE ROCKS” (for now)

Extrusive Igneous Rocks u Notes: Extrusive Igneous Rocks form 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

u Earth's Most Abundant Bedrock: 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 Rocks

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

How igneous rocks form… Extrusive When a volcano erupts or when magma bubbles to the surface Intrusive when magma cools slowly inside earth

Intrusive Igneous Rocks u Notes: 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 u Granite is also well-known from its many worldfamous natural exposures. These include: Stone Mountain, GA; Mount Rushmore, SD

Intrusive Igneous Rock Porphyry

Igneous Rocks u Notes: Texture – fine grained Rapidly cooling lava forms a finegrained 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 u Obsidian on the side of a volcano

Igneous Rocks u Notes: Texture: coarse-grained Slowly cooling magma forms coarsegrained rock with large crystals Ex: granite and porphyry

Igneous Rocks – Mineral Composition u Notes: When magma is high in silica lightcolored rocks form - like granite. When lava is low in silica darkcolored rocks form - like basalt

High Silica vs. Low Silica

Uses of Igneous Rock u Notes: u Granite – Statues, Bridges and old public buildings, Paving streets with cobblestone, floors, kitchen countertops (thin polished sheets of Granite)

Uses of Igneous Rock u Basalt - Gravel for construction u 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! u. Pumice polishing – used for cleaning and

Uses of Igneous Rock u Statues, Public Buildings - Granite

Uses of Igneous Rocks u Cobblestone streets, kitchen countertops – Granite

Questions… u What processes form Igneous Rocks? u How are the 2 types of Igneous Rock different? u How can we use Igneous Rocks? How have they been used in the past? u Can you describe the most common Intrusive Ign. Rock? Where is it commonly found? u Can you describe the most abundant Extrusive Ign. Rock? What area on Earth is mostly made of this type?