The images are those of common salt. The sample was taken by slightly dampening the clear sticker that goes onto the stage in order to make sure that the salt sticks to it. The individual salt crystals, under the foldscope lens, look almost like ice-cubes. They are transparent and colourless. While salt deposits, in the form of crystals up to several inches can be found in salt mines, the salt crystals used here (bought from a packet of salt at your average grocery store) are about 3*10-4m in length. Thus, the apparent size of these salt crystals is about 3-4 cm each. The backlighting used here is just the blank white screen of an iPad on full brightness.
The salt pictured above is Sodium Chloride (NaCl) and is one of the most common salts found just about anywhere (most commonly found on seashores due to the evaporation of sea water in deposits that are imaginatively known as evaporite).
We actually make use of Halite (which comes from evaporite deposits), which is naturally occurring Sodium Chloride, known simply as common salt. Salt actually makes up close to 78% of the sea water. For the longest period in human history, the only method of producing salt for human consumption was to evaporate large quantities of seawater and in many developing countries that have coastlines, it is still the primary method of production of salt, especially in countries closer to the equator, where the temperatures allow for the easy evaporation of sea water in basins that are made close to the coast lines
 Hills, J. (23 March 2020) Salt; Sodium Chloride. Encyclopaedia Britannica. https://www.britannica.com/science/salt