Crystal Formation

Aubree Niemiec e-mail: aln5076@psu.edu
Jessica Mitchell e-mail: jjm5363@psu.edu

This lesson is appropriate for grades 6-8 with a focus on elements and atomic structure as well as rock types and crystal formation.

The state standards that will be focused on are 3.5.7 B, building off of 3.5.4 B, along with standard 3.4.7 A and 3.7. In addition, state standards 3.1.7 C and 3.2.7 B will also be covered. The national standards included are Standard B part 1, D part 1.

1. Students will be able to define atoms and compounds.
2. Students will be able to define the three main types of rocks.
3. Students will be able to explain how crystals form and under what circumstances different sizes form or not at all.

Content Explanation:
There are three main types of rocks. The compacting and cementing of sediments at the Earth’s surface form sedimentary rocks. Sediments are particles of rocks or other materials that have been carried along and deposited. Igneous rocks are formed by molten lava or magma, while metamorphic rocks are sedimentary or igneous rocks that form as a result of chemical reactions, heat, and/or pressure.
All matter is made up of atoms, which are the basic building blocks of matter. When two elements combined, a compound is formed.
In a crystal, the atoms, ions, or molecules that make up the solid substance are arranged in an orderly, repeating, three-dimensional pattern called the crystal lattice. One way crystals can form is from the cooling of magma. When magma cools slowly beneath the Earth’s surface, large crystals form. However, when it cools rapidly, small crystals form. Furthermore, no crystals will form when molten rock reaches the surface of the Earth and cools too quickly. Another way crystals can form is from compounds being dissolved in a liquid. When the liquid evaporates, or changes to a gas, crystals are left behind. From this, we can gather that larger crystals form as a result of a solution cooling over a longer period of time, where smaller crystals form as a result of rapid cooling.

Materials, Equipment, Set-Up
  • (approx. 10 mL for each set-up) Salt
  • (approx. 25 mL for each set-up) Water
  • (5)Beakers
  • (3)Stirring rods
  • (3)Hot plates
  • (3)Dinoscopes
  • Rock samples
  • (6) Goggles
  • (3) Computers

Crystal Caves Rock Candy Recipe

Rock Candy is a delicious sugary treat that takes several days to form but only a short time to make! The sugar crystals form after sugar and water come to a boil and then the mixture cools. The crystals can be any size or color you want! Test out this fun, scientific candy.

2 c. sugar
1 c. water
Food coloring (optional)
Saucepan (beaker)
Pencil or wooden dowel (popsicle stick)
Paper towel

SAFETY: Risk of being burnt by a hot plate and boiling water. Use caution around set-up. Beakers will be hot when removing them from the hot plate. Goggles will need to be worn.
Students will use a hot plate to bring 25 mL of water to a boil over medium/high heat. When the water begins to boil, slowly add in salt until it will not dissolve anymore (point of saturation), stirring constantly. Once all dissolved, let the solution continue until all water has evaporated. Remove from the hot plate and observe crystal size using the dinoscope and compare to regular salt crystals. Next, students will be observing three different types of igneous rocks and how the rate of cooling time affects the crystal size.
(Actual recipes will be handed out to the students)

Read more: http://channel.nationalgeographic.com/episode/into-the-lost-crystal-caves-4636/rock-candy#ixzz12pFyeF7D

Body of Lesson
a) Engagement: (5 Minutes)
      • So who here likes candy?
      • Has anyone ever heard of rock candy before?
      • Do ever wonder how it’s made? Or why it looks the way it does?
      • What are the three types of rocks?
      • Do you know how they are formed? If so, explain.
(At this point the three rock types will be discussed.)
      • Of the three types, some contain crystal structures of different sizes.
(At this point elements and formation of crystals will be discussed.)

b) Exploration: What causes crystals to be of different sizes? (7 minutes)
      • We will explain to them how crystals are formed and what causes them to be different sizes. Our materials will be used in the formation of salt crystals. This will demonstrate how temperature and time affect crystal size. Students will start preparing the formation of crystals by dissolving salt in boiling water and evaporating the water off. The final products will be shown to them. Students will be given three types of igneous rocks to examine under the dinoscope. They will determine crystal size and predict how they formed. They will record data in the table provided.

c) Explanation: (3 minutes)
      • After the students complete the table, we will ask them to explain to us how they determined the results and help them by clearing up any misconceptions.

d) Evaluation: (5 minutes)
      • Students must identify the three types of rocks from pictures and explain why they classified them in such a way.
      • With having two crystals, a small and large one, students must explain why there is a difference in the size of the crystals.

e) Elaboration:
      • If there is extra time, we will go further into how rocks can be identified, e.g. layers, color, cleavage.
References:Maton, Anthea. Exploring Earth Science. Englewood Cliffs, NJ: Prentice Hall, 1995. Print. Wesley, Addison. Chemistry, 5th Ed. New York, New York: Prentice Hall, 2000. Print.