Growing & Observing Crystals
Within the branch of Geology, students learn about the mineral crystals that make up rocks. These crystals can be of different size and shape based on where they form, what they form from, and the amount of time allowed to form (cooling). In this investigation, students will grow their own crystals changing one variable, as compared to the "control" crystals, in order to determine the best "environment"/conditions to grow the best, largest crystals.
Context for Use
The type of salt used to grow the crystals will change the shape of the crystals you get. I usually use BOTH table salt and Epsom salt, as the table salt crystals are cubic and the Epsom salt crystals are needle-like. I use aluminum pie pans with black paper cut to fit the bottom, as the crystals stick to and stand out on the black paper.
Resource Type: Activities:Classroom Activity, Lab Activity
Grade Level: Middle (6-8)
Theme: Teach the Earth:Teaching Environments:K12
Description and Teaching Materials
You can begin with the question, what variables affect how crystals form ("Grow")? Discuss as a class, or as a lab group, etc. Then walk through the procedure for the lab. Talk about what the students want to change as their one independent variable, what is the dependent variable, what are the constants. You can choose to allow the lab groups to decide on their own variable or assign it. It can work both ways. Here is one way to assign groups:
Lab 1: double the table salt
Lab 2: double the water
Lab 3: leave the pan with solution sitting out
Lab 4: put the pan with solution in a bag
Lab 5: double the Epsom salt
Lab 6: double the water
Lab 7: leave the pan with solution sitting out
Lab 8: put the pan with solution in a bag
You could also have a group use warm water versus cold water, etc. Students may also come up with other variables to change.
According to the group's variable, they must write a hypothesis before they begin. They can write individually, or as a group.
Then, allow the students to follow the directions, mixing the desired amount of salt and water, pouring it into the aluminum pie pan (with black paper), and place in desired location. After 3-4 days, or a weekend, allow students to observe their crystals, drawing what they look like, comparing to the control, and writing a conclusion. What do they see? Was their hypothesis supported or refuted? What are any similarities & differences with other groups? Would more time have given them more or bigger crystals? Then talk about communicating these results. Who would want to know this, why? What are the IDEAL conditions for growing crystals? Students can write this up as a simple lab, see attached lab sheets; or students could write up their own, formal lab report or paper about the experiment. It can be taken/adjusted to any level desired. crystal growth lab (Microsoft Word 36kB Aug2 09)
Teaching Notes and Tips
8.III.A.3&6 –earth & space, earth structure & processes (rock cycle, identify & classify rocks & minerals)