Sal ammoniac

Sal ammoniac is a rare mineral composed of ammonium chloride, NH₄Cl. It forms colorless, white, or yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and a brittle to conchoidal fracture. It is quite soft, with a Mohs hardness of 1.5 to 2, and it has a low specific gravity of 1.5. It is water-soluble. Sal ammoniac is also the archaic name for the chemical compound ammonium chloride. The Romans called the ammonium chloride deposits that they collected from near the Temple of Jupiter Amun (Greek Ἄμμων Ammon) in ancient Libya 'sal ammoniacus' (salt of Amun) because of proximity to the nearby temple. Salts of ammonia have been known from very early times; the term Hammoniacus sal appears in the writings of Pliny, but it is not known whether the term is identical with the more modern sal-ammoniac. In any case, that salt ultimately gave ammonia and ammonium compounds their name.