Category Halide mineral Strunz classification 3.AA.25 Unit cell a = 3.859 Å; Z = 1 | Formula
(repeating unit) NH4Cl Space group Pm3m Crystal system Cubic crystal system | |
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m) | ||
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.
It typically forms as encrustations formed by sublimation around volcanic vents and is found around volcanic fumaroles, guano deposits and burning coal seams. Associated minerals include sodium alum, native sulfur and other fumarole minerals. Notable occurrences include Tajikistan; Mount Vesuvius, Italy; and Parícutin, Michoacan, Mexico.
Uses
It is commonly used to clean the soldering iron in the soldering of stained-glass windows. In both jewellery-making and the refining of precious metals, potassium carbonate is added to gold and silver in a borax-coated crucible to purify iron or steel filings that may have contaminated the scrap. It is then air-cooled and remelted with a one-to-one mixture of powdered charcoal and sal ammoniac to yield a sturdy ingot of the respective metal or alloy in the case of sterling silver (7.5% copper) or karated gold.
Sal ammoniac has also been used in the past in bakery products to give cookies a very crisp texture, but that application is rapidly dying from the general disuse of it as an ingredient. However, in some areas of Europe, particularly Nordic countries and the Netherlands, it is still widely used in the production of salty licorice candy known as Salmiak, or Salmiakki.
Sal ammoniac (ammonium chloride) was the electrolyte in Leclanche cells, a forerunner of the dry battery; a carbon rod and a zinc rod or cylinder formed the electrodes.
