The Diversity and Cycle of Rocks

Rock Cycle

Rock cycle: describes dynamical transformation of rocks between the 3 rock types

• IGNEOUS, METAMORPHIC, SEDIMENTARY

Where are we going?

• What is the Earth made of? (Of what is the Earth made?)

• When compounds organize into crystalline structures….Minerals, otherwise amorphous!

• Minerals combine to form Rocks

Abundance of Elements in the Earth’s Crust

• 98% of the mass of crustal minerals is from 8 elements

Crystals of a MineralAragonite - CaCO3

Minerals

Mineral: building blocks of rocks

• Naturally occurring

• Homogenous

• Inorganic solid (biominerals okay)

• Fixed crystalline structure

• Definable chemical composition

Quartz (SiO2)

Crystal Structure isdefined by the orderingof atoms which form acrystal lattice

This arrangement produces distinct and and identifying properties of the mineral.

-Cleavage-Hardness-Crystal Habit

Cleavage

Mineral Properties

• Crystal Form or Habit• Cleavage • Hardness• Color• Luster• Specific Gravity• Streak• Other Features

• Natural Shape• Broken Shape• Soft or Hard• Clear to Colored• Metallic or Non-• Density=mass/volume• Color of powder• Reaction with acid

Crystal Form or Habit

Polymorphs – many shapes

• Same chemical composition

i.e., mineral composed of Carbon

• Different arrangement of atoms in the crystalline structure

C: Diamond versus Graphite

CaCO3: Aragonite versus Calcite

Bonding of Atoms into an Ordered Crystalline Structure

Arrangement of Atoms Defines Crystal Properties

Valence of the Silicate Ion or TetrahedronThe basic building block of all silicates

More Complex Silicate Minerals

Pyroxene Amphibole Micas

SiO3-2 Si4O11

-6 Seriously Complex

Tectosilicates – Framework Structure

•Quartz•Feldspars

Common Earth Minerals

• Olivine• Pyroxenes• Amphiboles• Micas• Feldspars• Quartz

• Isolated• Single Chain• Double Chain• Sheets• Framework• Framework

Sequence of CrystallizationBowen’s Reaction Series

EXTRUSIVE INTRUSIVE

Igneous Rocks

Igneous rocks: most abundant rock type

• Formed from freezing of magma

at temperatures between about

650-1100 °C

• Intrusive rocks

- Slow cooling within the Earth

• Extrusive (volcanic) rocks

- Erupted on the Surface

Addition of Water Results in Partial Melting Formation of Felsic and Intermediate Magmas

Igneous Rocks

Igneous rocks: classified by mineral size and composition

• Intrusive rocks

- Crystallized slowly

- Minerals are larger

• Extrusive rocks

- Crystallized rapidly

- Minerals are smaller

Granite

Rhyolite

Obsidian Glass

Intrusive Extrusive

IGNEOUS ROCKS – RATE OF COOLING

Rocks Types

• Rock types are categorized by their genesis

• Igneous rocks: crystallized from (partly) molten material

• Metamorphic rocks: recrystallized under intense temperature and/or

pressure

• Sedimentary rocks: lithified fragments of pre-existing rock or formed

from biological/chemical precipitation

Rocks: aggregates of minerals

IGNEOUS ROCKS

METAMORPHIC ROCKS

SEDIMENTARY ROCKS

RELATIVE ABUNDANCE OF ROCK TYPES

SUMMARY