Rocks. Who knew?

This week’s demo: grading the hardness of minerals using the traditional scratch test.

Examples:

Talc cannot scratch quartz, but quartz can scratch talc

Quartz cannot scratch diamonds, but diamonds can scratch quartz (etc)



I figured after all the excitement with fires and fizzes in recent demos, this one might achieve a collective yawn. Not so: everybody seemed fascinated by the idea. The more tests I did, the more the voices rose “now try the sandpaper on the steel! Now try the limestone on the chert!”. Scratching rocks together: who knew? I remember coming into class with high hopes about the size-of-the-solar-system demo, only to find practically no resonance. It’s easy to infer a simple rule such as that lessons are better “if I can touch it and see it”, but that doesn’t explain their excitement about imagining what is a googol, or how many molecules in a teaspoon, or the habits of pangolins.



As the year proceeds, I flatter myself that I am gradually improving my basic classroom-control tactics. Of course I don’t have the Black Magic Secrets that enable certain Montessori teachers (hint: first initial "D") to whisper “Children: Quiet” and bring a roomful of tornadoing screamers to a sudden frozen silence and rapt attention, but still I fancy the class is doing pretty well at remaining focused and seated in circle. Which brings up our little mini-anecdote: I had brought in a pair of safety glasses (“always wear these when breaking rocks with a hammer”). Just as I was congratulating myself on my Well Managed Group, one boy [name omitted] puts on the safety glasses: then, apparently fancying himself to be something like Bud The Spaceman with the glasses on, he takes off at about 100mph on hands and knees, giggling wildly. At this point two others pursue him (surely planning to restore order by open-field-tackling the perpetrator). For a moment it looked pretty dicey. I did manage to get everyone back to circle fairly quickly, but it was a good reminder about how close we are to the edge at every instant.



Questions from the Question Box included

How big is the world’s biggest tidal wave (I don’t know, so I dodged into How Earthquakes Make Tidal Waves and Tsunamis Is Another Word For Tidal Wave. I thought it would be dull to get into measuring tidal waves by height, mass, distance of dispersion …)

How thick are your teeth? (I didn’t know, so I brought in a digital caliper/micrometer the next day. Incisors are 3mm thick and molars 12mm. I am sure I looked pretty comical jamming a caliper into my face).