Potassium is another element whose name is familiar to most but few have actually seen. When great care is taken to separate a very pure sample of potassium it appears as shiny as the silver backing of a mirror. For that level of conservation you would need to store it under vacuum or an inert gas because otherwise it would very quickly oxidize. Even when stored in inert mineral oil traces of contaminants are enough to spoil the surface finish and turn the metal whitish purple (which is kind of attractive as far as corrosion goes!)
Potassium is also very light and will float on water. Except doing so would be foolish, least of all because it would ruin your precious sample! A metal chunk thrown in water will immediately catch on fire and then explode releasing toxic but admittedly quite colorful byproducts!
This offering has three options. Cheapest is a piece of bare potassium in gel. Because of its high reactivity the potassium may react with tiny impurities in the gel to form surface oxides and/or little bubbles but this is the cheapest option and the one where you get the most for the least. Next up is a tiny lab-made ampule containing an estimated 15mg of the metal and a bigger ampule of about 100mg.