What do rocks tell us about the Earth?

Formed from the cooling and crystallization of magma

Magma – Molten rock beneath the Earth’s surface (800 -1200°C to melt rock)

Lava – Magma that flows out onto Earth’s surface

Very similar to elements found in Earth’s crust

O, Si, Al, Fe, Mg, Ca, K and Na

Silica - Most abundant

What is wrong with this picture?

Extrusive Igneous Rocks• Fine grained

igneous rocks that cool quickly on Earth’s surface

ObsidianExtrusive

Small CrystalsCooled Fast

GraniteIntrusive

Large CrystalsCooled Slow

• Intrusive Igneous Rocks

– Coarse grained igneous rocks that cool slowly beneath Earth’s surface

Felsic (Granitic)• Light colored, High silica content, contain

quartz and feldspars

Felsic Igneous Rock

Mafic Igneous Rock

•Mafic (Basaltic)

–Dark colored, rich in iron and magnesium

•Ultra Mafic

–Low silica content, very high levels of Fe and Mg

Porphyritic Rocks• Rocks characterized by large well-formed crystals

surrounded by fine grained crystals of the same mineral

Vesicular Rocks • Spongy looking rock whose gas bubbles have broken

Partial Melting• Process where some minerals melt at low

temperatures while other minerals remain solid (Melting Points)

• Example: Ice Cube and Wax Candle

Fractional Crystallization• Process where different minerals form at

different temperatures

Bowen’s Reaction Series• Predictable, dual branched pattern in which

minerals crystallize from cooling magma

Veins• Igneous rock intrusions that contain ores (Au and Quartz)

Pegmatites• Vein deposits of extremely large grained minerals (Li and

Be)

Kimberlites• Rare, ultramafic rock that can contain diamonds and other

minerals formed only under very high pressures

Compare and Contrast magma and lava.

What two types of igneous rocks are formed as each cools?

Describe the three major mineral groups of igneous rocks. What minerals are found in each?