I have these white stones that give off a strong sulphur-like smell when struck together to produce a spark (triboluminescence). This is mostly due to hydrogen sulphide as suggested by many sources such as: https://www.mineralseducationcoalition.org/sites/default/files/scratch_sniff_minerals_0.pdf
By the way, I’ve also noticed that some water-rounded white quartz pebbles sold as landscaping rocks will, when knocked together, give off a sulfurous odor. This is probably due to a slight amount of hydrogen sulfide in their fluid inclusions, too.
The smell persists for a few minutes after the stones are struck together. Obviously, the trapped gas is released from the gaps in the silica crystallites but why the odour lingers is puzzling. Is it because $H_2S$ is more viscous than air that it stays near the surface of the stones? Or is it adsorption of the gas on the surface? Or both? Or a different mechanism?
I want to develop this as an inquiry question for school students as it is something very tactile that involves many physical concepts.