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.

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•. Minerals form in a process called crystallization • 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 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 • 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 • 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 • 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 • 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 • 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.