How Minerals Form

Section 3.2

Key Questions

How do minerals form from magma and lava?

How do minerals form from water solutions?

Key Terms

geode

crystallization

magma

lava

solution

vein

Key Concept:

Minerals form as hot magma cools inside the crust, or as lava hardens

on the surface.

When these liquids cool to a solid state, they form

crystals.

Star Fleet Academy

• Minerals form in a process called crystallization.

In crystallization, particles of a substance

form crystals.

Remember, crystals are solids that have their

particles lined up in repeating patterns.

Crystals have flat sides and sharp edges.

Many minerals form when magma or lava cools.

Magma is melted material inside Earth.

Lava is magma that reaches Earth’s surface.

• When magma cools deep under Earth’s

surface, it cools very slowly.

The crystals that form are very large.

• When magma cools closer to the surface, it

cools faster.

The crystals that form are smaller.

• When magma erupts to the surface and forms lava, it cools even faster.

The crystals that form from lava are very small.

Minerals From Solutions (pages 77–79)

Key Concept:

When elements and compounds that are dissolved in water leave a solution, crystallization occurs.

• Substances that form minerals may be

dissolved in water.

“Borax Lake”

The water and dissolved substances form a

solution.

A solution is a mixture in which one substance is dissolved in another.

Some dissolved substances form mineral crystals when

they leave a solution.

Dissolved substances can leave a solution in two

ways.

• Dissolved substances can leave a solution when

the solution evaporates, or turns into gases.

This happens on Earth’s surface.

For example, the mineral halite formed when ancient

seas evaporated.

• Dissolved substances can leave a solution when

the solution cools. This happens below Earth’s surface. Underground

water heated by magma dissolves many substances.

When the water cools, minerals come out of the

solution and form crystals.

• A vein is a narrow band of minerals that lies

between rock layers.

Veins look like streaks of fudge in vanilla fudge ice

cream.

Veins form when solutions of hot water

flow through cracks and then cool. Silver is a

mineral that may form in veins.