Photographs are the usual means, but are limited in how much they can convey. There is no movement or change of colour, you cannot 'explore' the slide by moving around it and trying different focus and other settings.
At Geosec we are currently experimenting with video, zoomable pictures and other ideas as much as time permits when not actually making the next batch of slides for sale. An interactive software program, the Geoscope, was tried, but ran into problems with the web browser programs that the program ran in, being automatically updated and stopping it working.
Ammonite from Madagascar
So, still work in progress....