Fluorite

Splashery stretches a drumhead over this Splash's outline, twelve inches across, and finds the ways it can ring. Its lowest is 315.3 Hz, 23 cents sharp of E♭4. The next fifteen are its overtones, and each one draws its own figure: sand gathers on the lines that stay still.

Tap it to switch on the ultraviolet lamp; drag to turn it.

A specimen of fluorite, scanned and drawn with splats. Fluorite is calcium fluoride and grows in cubes. Under ultraviolet light many fluorite crystals glow blue-violet: the word fluorescence comes from this mineral.

Tap it and the lamp comes on: the stone turns slowly in its glow, then the lamp goes off. Drag to turn it and look for the cubes that grew into one another as the crystal formed.

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