Not only are these beautiful and soothing to look at, they help to naturally cleanse the air through their emission of negative ions (in this case, negative is a positive thing!). They purify the air through a process called hygroscopy, where they attract and absorb water molecules from their surroundings. As the salt warms up from the heat produced by the flame inside, that same water then evaporates back into the air and the trapped particles of dust, pollen, smoke, etc remain locked in the salt.
These candle holders vary in appearance. Approximately 9cm tall.