Mineral Formation

6th Grade

Popcorn Rock Activity

• When the rock dolomite is doused in white distilled vinegar, aragonite crystals slowly form

A similar process occurs in Yellowstone National Park and in the Carlsbad Caverns in New Mexico

Carlsbad Caverns, New Mexico

Stala…WHAT?!

StalagMITE = on the ground –mighty and tall

StalacTITE = hanging from the ceiling –hanging tight to the ceiling

These form similarly to the “popcorn rock”

• Acid rain or water from other sources reacts with the rock such as limestone or dolomite

• This reaction hardens into a mineral

• “Popcorn rocks” appear on cavern walls, such as at the Lehman Caves

Lehman Caves

Crystals that often form from water added to rock are usually calcite and aragonite

What are 3 ways that minerals form?

• 1) form by magma and lava cooling

• 2) form by hot water solutions – solutions: elements and compounds that are

mixed with water

• 3) form by solutions evaporating

What is this called?

Geode = a rounded, hollow rock that is often lined with mineral crystals

Geode: How is it formed?

Formed when….• 1) a cavity forms in a rock –(an open space,

similar to a shell) –usually happen with rocks that are made from lava (the empty space is the gas bubbles)

Geode –crystals form when water containing dissolved minerals seeps into a crack or hollow in a rock

Minerals from Solutions

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

1) Minerals formed from Evaporation

• Minerals form when solutions evaporate

• Ex. If you stir salt crystals into a beaker or water, the salt dissolves, forming a solution. Eventually the solution evaporates, leaving behind salt crystals

• Ex. mineral halite formed over millions of years when ancient seas slowly evaporated– This happens in the US along the Midwest, Southwest, and

along the Gulf Coast

Halite –we use it in every day life!

Halite = table salt

Minerals formed from evaporation --gypsum

Minerals that can be formed by evaporation --Calcite

2) Minerals from Hot Water Solutions

• Deep underground, magma heats water to a high temperature

• When the water solution begins to cool, the elements and compounds leave the solution and crystalize as minerals

• Often PURE metals are formed this way

Minerals from Hot Water Solutions

• Vein = a narrow channel or slab or a mineral that is different from the surrounding rock

Gold Vein

• Remember that PURE METALS tend to form from hot water solutions underground, forming veins

• Ex. Gold, Silver, Platinum

Platinum

• Luster: metallic• Fracture: hackly • Hardness: 4.5• Streak: silver-grey• Cleavage: none

Silver

• Luster: metallic• Fracture: hackly• Hardness: 2.5 – 3• Streak: silver-white• Cleavage: none

3) Minerals formed from magma and lava:

• Minerals form: – As hot magma cools inside the crust– As lava hardens on the surface *When liquids cool to a solid state, they form crystals.

Tourmaline: a mineral that forms as magma cools deep beneath the surface

What influences the size of crystals?

The size of crystals depend on:

• The rate at which magma cools • The amount of gas the magma contains• The chemical composition of the magma

Magma closer to the surface cools FASTER (smaller crystals)

Magma deep within the crust cools SLOWLY (bigger crystals)

The size of a mineral depends on whether its high or low in the crust

• Large crystals –deep within the crust

• Small crystals --near the surface

http://www.youtube.com/watch?v=0OLdSJmvcUs

• Take a look!