Un-reconstructed slob?

You're probably right...

OK - having rinsed out my cafetière I never dry it, being in too much of a hurry to dose it with coffee, light the gas under the kettle, find my mug & put in 1.5 tspoons of sugar...

By this time the kettle's trying to boil it's lid off - pour it on the coffee.
The boiling water almost instantly dries the droplets left from the rinsing leaving a deposit of calcium carbonate...

Thing is - I'm fascinated by the regularity of the chalk deposits - they produce a most pleasing pattern!!

Any ideas how this might be?