The term 'soft white mineral' can be described by two crossword solutions: HALITE (6 letters) and BORAX (5 letters). HALITE is a mineral composed of sodium chloride, commonly known as rock salt. It is typically colorless or white, but can also be found in shades of blue, pink, yellow, and red. BORAX is a naturally occurring mineral composed of sodium borate, which is a combination of boron, oxygen, and water. It is often used as a cleaning agent and has a soft, white, powdery texture.