Let’s Review…5 Characteristics

• 1. Naturally occurring (why won’t a cake work…?)

• 2. Inorganic (can it come from once living things?)

• 3. Solid (how about a liquid or a gas?)

• 4. Crystal Structure (look at it under a microscope)

• 5. Definite Chemical Composition (can a mineral contain rocks…?)

Properties…

• Color

• Streak

• Luster

• Density

• Hardness

• Crystal System

• Cleavage/Fracture

• Special Properties

• Picture, Rock collecting

Egg-shaped rock about the size of a football…

Geode

oGeodes are formed when water containing dissolved minerals seeps into a crack or hollow in a rock

oCrystallization happens lining the inside of the rock with crystals that are often perfectly formed.

What is crystallization?

• Geode pictures

• Crystallization – the process by which atoms are arranged to form a material with a crystal structure.

What kind of crystal structures can we have?

• Crystallization picture

• Crystal gardens?

Factors that affect crystal size:

• Amount of gases present

• Chemical composition

• Rate of cooling

Two types of mineral formation:

• Crystallization of magma and lava

• Crystallization of minerals dissolved in water

Minerals from magma & lava…

• What’s the difference between magma and lava?

Magma = below the earth’s surface

Lava = above the earth’s surface

• magma

Magma = Underground

Magma = Underground

• lava

Lava = Above Ground

Lava = Above Ground

Slow Cooling…

• Magma hundreds of miles below the surface can take many thousands of years to cool.

• Slow cooling leads to the formation of very large crystals– Slow cooling allows atoms to be added

according to a regular pattern

• Slow cooled crystals

Mineral crystals grow under a variety of conditions. Slow cooling of magma (melted rock) deep within the Earth generally leads to a rock such as granite with visible crystals of feldspar, quartz, mica, amphibole and other minerals. Water in the magma can even facilitate pegmatite formation. Pegmatite is an igneous rock composed of mineral crystals generally with a diameter of several centimeters which, on rare occasions, can be meters.

Fast Cooling…

• Magma close to the surface or lava at the surface cools much more quickly

• Rapid cooling means the molecules don’t really have time to form large crystals– Do they form a pattern at all?

• Fast cooled crystals

Minerals from solution…

• Solution – a mixture in which one substance is dissolved in another

• What happens when those compounds come back out of the solution?

• How would these compounds come out of solution?– Minerals can form this way underground and

in bodies of water.

Evaporation…

• Halite

Also…

• Gypsum

• Calcite

Hot water solutions…• Pure metals that crystallize can dissolve in

hot water solutions and flow through cracks in rocks to form veins

• Copper

Also…

• Silver

• Gold

• Vein pictures