FeCl3 – iron(III) chloride – crystals’ color depends on the viewing angle. They can be purple, green, brownish-reddish, or dark brown with a metallic luster. Their yellowish tint when interacting with air lends them a resemblance to wet sand. Iron(III) chloride is utilized in sewage treatment and the production of drinking water. In water, ferric chloride forms a slightly soluble iron hydroxide; during its formation, various organic and inorganic impurities are captured, forming loose flakes that are easily removed from the treated effluents. Pure iron(III) chloride has strong acidic properties, and it is often used as a catalyst in organic synthesis.