Higher iron, sulfur and magnesium mineral content gives them their darker color and they have a much softer glow than pink or white salt lamps. Gray rock salt lamps, also sometimes called black salt lamps, are best for bedrooms where you don’t want too much light.Perhaps even more rare than white rock crystal lamps are the unusual dark gray salt lamps from the Bahadur Khel salt mine in Pakistan.Higher iron, sulfur and magnesium mineral content gives them their darker color and they have a much softer glow than pink or white salt lamps.Gray rock salt lamps, also sometimes called black salt lamps, are best for bedrooms where you don’t want too much light. They could even make a beautiful night light in the children’s bedroom.