Rocks and MineralsLesson 7 Part II BIG IDEA: Rocks and minerals have properties that can be: observed, tested, described, identified and recorded.
Kit Inventory • What does the object look like? • Where have you seen it before? • What is it used for? • What do you think it is?
Part II: Growing Crystals We recently learned that crystals are present in minerals as one of 6 shapes. Geologists can use the crystal shapes found in minerals as an identification tool because the same pattern of crystals will be present in that mineral no matter where it is found. Today we are going to use the materials our geologist has sent to start investigating one of the ways crystals are formed.
Focus Question How are crystals in minerals formed?
Prediction I think we can use the materials the geologist has sent to make our own crystals if we… because…
Word Wall Naturally, crystals are formed in one of two ways and these two processes are referred to as crystallization. Crystallization The process by which crystals are formed. When molten minerals solidify or when minerals are deposited from evaporated solutions. Unfortunately in a classroom setting we don’t have the ability to watch minerals crystallize when melted rock solidifies, but we can observe the formation of crystals by evaporation. Evaporation The conversion of a substance from a liquid to a gaseous state.
Evaporation I know you have all experienced or observed in some form the evaporation of water. When a liquid such as water evaporates it changes from a liquid state to a gaseous state. The solid particles in that liquid cannot be turned into a gas so they are left behind. Have you ever noticed how a puddle of water will often be replaced with a ring or stain when the water has dried up or evaporated? The stain left is made up of the solid particles often called sediment... sand, dirt, tiny rocks, minerals, etc. that were mixed in with the liquid. The solid particles left behind could crystallize.
Crystallization Many of us had a very difficult time identifying the shape of the crystals found in our samples. Part of the problem was because the crystals were too small to see with our magnifiers. If all crystals of a particular mineral have the same shape than why are some crystals larger than others? The size of the crystal is determined by how fast it is formed. The faster a molten material cools, or a solution evaporates, the smaller the crystals will be. The slower the molten material cools, or a solution evaporates, the larger the crystals will be.
Growing Crystals Before we begin to form our crystals I would like you to reflect back to the salt crystals I showed your groups. What shape were these small crystals? We are going to dissolve salt crystals into a solution and see if we can recrystallize them through evaporation. • Prediction • What shape do you think the crystals you form will be and explain your reasoning?
Data Collection We will observe what happens to our solution and add details to our science notebook. Each time we make an observation we should include an accurate drawing and description.
Making Meaning Conference • How are crystals in minerals formed? • Molten minerals solidify • Evaporation - Minerals are deposited from liquid solutions • How can minerals be identified by the shape of their crystals? • Minerals contain crystals and there crystals can only be one of 6 shapes. • Why were the crystals we created cubic? • Salt is a mineral and it’s crystals are cubic. Salt will always have cubic crystals no matter were it is found and how it is formed. • Why are some crystals larger than others? • The size of a crystal is determined by how fast it is formed. Slow = Bigger Crystals, Fast = Smaller Crystals
Claims and Evidence Based on what you have learned from your investigation of crystals, you need to record at least 3 claims and evidence statements in your science notebook. I claim that… I know this because… Possible Examples: I claim that all minerals contain crystals I know this because… I claim that you can identify minerals by the shape of their crystals. I know this because…
Reflection and Conclusion • What did you learn…? • What really surprised you…? • What new questions do you have…? • What would you like to know more about…?