Igneous Rocks

Chapter 5

Vocabulary

• • • Radioactivity-

the spontaneous process through which unstable nuclei emit radiation.

Lava-

magma that flows out onto Earth’s surface.

Igneous rock-

rocks formed from the crystallization of magma.

Vocabulary

• • • Partial melting-

solids.

the process by

which some minerals melt at low temperatures while other remain

Fraction crystallization-

the process by which different minerals from at different temperatures.

Bowen’s Reaction Series-

mineral formation.

a model that describes the relationship between cooling magma and

Composition and Origins of Magma

I. Composition of magma A. Magma is

a mixture of molten rock, gases, and mineral crystals.

B. The elements in magma are

the eight major elements in Earth’s crust.

1. The most abundant compound in magma is

Silica (SiO 2 ).

C. Magmas are classifies as

basaltic, andesitic

, and

rhyolitic

.

1. Their classification depends on

how much silica they contain.

Composition and Origins of Magma

Temperature Pressure Increase with depth In Earth’s crust.

This is known as the geothermal gradient.

Factors in the formation of magma Increases with depth under the surface Which increases the melting point of rock Water content Mineral content As this increases, the melting point decreases

.

Different minerals have different

melting points.

How Rocks Melt

When a rock begins to melt, the minerals with the lowest melting point melt first. The elements in these minerals from the liquid part of magma. As other minerals melt, the elements in those minerals are added to the magma and change its composition. The opposite happens as the magma cools. The elements in the minerals are removed from the magma in the order that the minerals crystallize, which is fractional crystallization.

Bowen’s Reaction Series

Partial Melting

Partial melting is when different minerals within a rock melt at different rates. When different minerals are melted new elements are added to the magma mixture changing the chemical composition.

Synthesize

Both branches show that minerals from in predictable patterns in cooling magma. However, in the right branch, the feldspar minerals undergo continuous change. The iron magnesium minerals, in the left branch, undergo abrupt changes.

Section 5.2 Vocabulary

Magma-

molten material found under Earth’s surface.

Intrusive Rock-

Igneous Rock that cool slowly beneath Earth’s surface.

Extrusive Rock-

Igneous rock that cool quickly on Earth’s surface.

Granitic Rock-

Light-colored rock high in silica and contains quartz and feldspar.

Basaltic Rock-

Dark-colored rock low in silica and contains iron and magnesium-rich materials.

Section 5.2 Vocabulary Cont.

Texture-

the size, shape, and distribution of crystals or grains that make up a rock.

Porphyritic texture-

characterized by large, well formed crystals surrounded by finer-grained crystals of the same mineral or different minerals.

Vesicular Texture-

A spongy appearance caused by broken gas bubbles

Pegmatite-

veins of extremely large grained minerals.

Kimberlite-

a rare, ultramafic variety of peridotite that forms pipe like structures and which sometimes contain diamonds.

Types of Igneous Rock

Intrusive -Coarse grained -Cool slowly -Form beneath surface Ex. granite Igneous Rocks Formed by crystallizat ion of magma Extrusive - Fine-grained - Cool quickly - Form above surface - Ex. Rhyolite

Mineral Composition _______________________________ 2. obsidian: ______________________________ __________________________ A coarse-grained rock that is mostly ____________________________

Grain Size Describe the conditions that cause igneous rocks to form large grains or no visible grains.

Intrusive igneous rocks are formed when magma cools slowly beneath Earth’s surface, so large crystals have time to form. Extrusive igneous rocks cool quickly because they are exposed to air and moisture on Earth’s surface, so visible crystals do not have time to form.

Igneous Rocks as resources List two characteristics of igneous rocks that make them good building materials.

1. They have interlocking grain textures, which give them strength.

2. They contain minerals that are resistant to wearing.

Ore Deposits The fluid from which Magma crystallizes Contains high levels The fluid fills

The fluid solidifies to form ____________ containing Metals such as _____, lead copper Rare elements such as Answer the synthesize question.

Other Information

Igneous is Latin for “from fire”