The silicon atom in its formula would normally require its classification as a silicate mineral. But some classification schemes prefer to place howlite with other borate minerals in the carbonates class because it has five borons to only one silicon and that its character and formation are more in line with other borate minerals such as colemanite , ulexite , borax and kernite . Color is white with gray to black streaks, web-like markings and blotches. Transparency crystals are opaque to translucent. Cleavage is absent.
Fracture is conchoidal to uneven.
Streak is white. Sometimes fluoresces a blue, yellowish white or off white color under shortwave UV light and dissolves in hydrochloric acid solution without bubbling. Associated Minerals include colemanite , ulexite , anhydrite , gypsum , colemanite and clays . Best Field Indicators are nodular character, color, solubility in HCl, luster, lack of cleavage and softness.