Mineral Properties -- Learning through Experience
Students are asked to come pick up a mineral in a box – open the box – handle and observe the mineral – and then locate all the other individuals in the room with that same mineral. Students are told that there are exactly 5 distinct minerals, and that when students think they've created a group of 3 matches, they should contact the professor for confirmation. The professor confirms that they have a match and then moves the group to a particular location in the room and instructs the remaining students to be sure to check with this group (group #1) to see if they have the same mineral. Meanwhile, all those in group 1 need to help folks find them AND come up with a verbal list of what characteristics their mineral has in common. The same occurs for Groups 2-5 until everyone has located their correct group.
The five minerals that I use in this exercise are calcite, quartz, gypsum, halite, and fluorite. I include samples in all colors and forms. I have to frequently tell those who are really lost to go to each of the groups, as they identifiy themselves and check to see if they belong. Once everyone is assigned to a group (and I've checked to confirm they're in the right group), I get members of each group to call out what their shared properties are (in any terms they like). Eventually we get color, luster, crystal shape, cleavage/fracture, transparency/opacity, and hardness covered.
Context for Use
Description and Teaching Materials
For calcite, I pick samples of many colors and clarity. But I always make sure that the rhombohedral shape appears at least partially in all samples.
For quartz, I look for samples that show at least a partial crystal, preferably with some conchoidal fracture.
For gypsum, I look for samples of all crystal shapes and clarity. Since hardness it he key here, I don't worry about them always looking the same.
For halite, it's the easiest one – the cubic form is enough.
For fluorite, I look for samples that clearly show a triangular cleavage face. Again, I look for all colors.
No other materials are necessary. The entire activity usually takes about 15 minutes tops.
During the call-out reporting portion of this activity, I usually stand up in the middle of the groups and guide them a bit. I'm looking for them to report out key aspects of their mineral, and if they don't mention one of them, I might coax it out of them. I also make sure they learn the proper names of these minerals.
Quartz – they often need help with the language of the crystal shape – but I encourage them to use regular language – a long crystal with how many sides? What happens at the top? Was color useful? When it breaks, are there flat planes? Can you tell the difference between the way it grows and the way it breaks? Does it reflect light in a similar fashion (even though colors might be different)?
Gypsum – Color is useful here – but it's mostly the luster of the surface that catches their eye – plus all the scratch marks left from those who have used these minerals before. After they announce it can be scratched with a fingernail, I ask everyone else to try to do the same with their own minerals.
Halite – Color and shape are the best characteristics here. And usually there are a few brave souls willing to taste it.
Calcite – rhombohedron, which I refer to as a skewed cube. Often they think that they have a cube like Halite, so I have to stress the right angles of Halite, and then they see it. Color unimportant. I mention here that the clear forms display double refraction. Usually one of the samples will show that. I also mention the acid test, but don't let them use it here.
Fluorite – I always leave this to the last. The luster is very similar amongst all the samples, while the color varies widely. But it's the triangular cleavage faces that bring it home. I also mention the black light.
When all is done, I have them bring their boxes back to the front and put them on a table in their groups, so folks can come up later and review the variations. (Boxes are clear plastic.)