Igneous Rocks

Igneous: “Ignis” Latin for Fire Magma – molten rock inside the earth Intrusive rocks Cool slowly below ground Generally course- grained

Intrusive IN - means? Related words that also have “IN” as a prefix?

Intrusive Rock Examples

Igneous: “Ignis” Latin for Fire Lava – molten rock outside the earth Extrusive rocks Cool quickly above ground Generally fine- grained

Extrusive EX - means? Related words that also have “EX” as a prefix?

Extrusive Rock Examples

What is Magma? Slushy mix of: molten rock gasses mineral crystals

Types of Magma Based on percentages of the mineral silica

Why is Magma Molten? Rocks melt between 800º C and 1200 º C Heat from earth’s formation Decay of radioactive elements

Factors Affecting Magma Formation Temperature increases with depth Called “Geothermal Gradient”

“Geothermal Gradient” Geo = Thermal = Gradient = Related words - gradual, grade

Factors Affecting Magma Formation Pressure increases with depth

Factors Affecting Magma Formation Water and Mineral Content more water, lower melting temp

How Rocks Melt Partial Melting Some minerals melt, others stay solid Result of different melting temperatures Candle wax and ice example

Partial Melting Example

How Rocks Melt Fractional Crystallization Some minerals solidify, others stay liquid Result of different crystallization temperatures Occur in opposite order of partial meting

Bowen’s Reaction Series As minerals cool, minerals form in a predictable order

Bowen’s Reaction Series Right Branch: Feldspars  Start as calcium-rich  End as sodium-rich Left Branch - Iron-Rich Minerals  Abrupt changes when cooling

Bowen’s Reaction Series Crystal Separation  Crystals separate out of magma  Results in minerals like Olivine, Pyroxene, Amphibole, Biotite Mica  Quartz remains as last mineral to form

Bowen’s Reaction Series Quartz is last mineral to form Often squeezed into veins in cooled rock

Classifying Igneous Rocks Extrusive or Intrusive

Classifying Igneous Rocks Extrusive or Intrusive Felsic Intermediate Mafic

Classifying Igneous Rocks Felsic Light-colored High in silica

Felsic Example: Pegmatite Intrusion

Classifying Igneous Rocks Mafic Dark-colored Low in silica Rich in iron and magnesium

Mafic Example: Basaltic Intrusion

Grain Size Non-Crystalline No visible grains Glassy texture Examples: pumice, obsidian

Grain Size Fine-Grained Less than 1 mm Examples: rhyolite, basalt

Grain Size Coarse-Grained 1 mm to 10 mm Examples: granite, gabbro

Grain Size Very Coarse-Grained 10 mm or larger Example: pegmatite

Mineral Composition 2. Examining a “Thin Slice” Thin Section of Basalt, an igneous rock. Different colors indicate different minerals.

Vesicular Textures What would happen if the foam above the bottle solidified instantly? What would the resulting solid look like?

Vesicular Textures Result from very fast-cooling lava that contains dissolved gasses Example: scoria, pumice

Exceptions to the General Rules Porphyritic Texture larger crystals scattered among much smaller crystals. Cools in two stages- cooling rate changes from slow to fast. ● Porphyritic granite

Igneous Rocks as Resources Most igneous rocks are hard, dense, and durable. These rocks make good tools and building materials. Contain Ore deposits - a useful substance that can be mined for profit. Pegmatites - contain large mineral crystals Kimberlites - diamonds form here