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Feather-Like Sal Ammoniac Formation
HALIDES · ISOMETRIC

Sal Ammoniac

NH4Cl

Hardness
1–2
Streak
White
Spec. Gravity
1.5
System
Isometric

About

Sal ammoniac is one of the few minerals composed of ammonium (NH4), and it is the best known of the ammonium-bearing minerals. It forms in natural fumaroles, where gas vents from underground from volcanic activity. It also forms from the process of the burning of coal in coal deposits. The formation of Sal ammoniac is unique, as it is created from sublimation, meaning it crystallizes directly from gaseous fumes and bypasses a liquid phase.
Sal ammoniac is highly soluble in water, and crystals can only be collected prior to a rainfall after their formation. A heavy rain will be enough to disintegrate an exposed Sal ammoniac crystal. In addition to its solubility, Sal ammoniac crystals can also be very delicate, and care should be exercised when handling them.
Sal ammoniac is easily synthesized. However, its natural crystal formations are unique in habit, unlike any other mineral. This, combined with its remarkable mode of formation, and its odd composition, make this a most unique mineral.
Sal ammoniac was named by the ancient Romans, who collected this material near the temple of Jupiter Ammon in Egypt, thereby calling it the salt [sal] of Ammon [ammonocius]. The name of the chemical compound ammonia was subsequently derived from Sal ammoniac.

Crystal Forms & Aggregates

Most famous for its snowflake, feather-like, or skeletal-like crystals branching off a central dendritic spine. These unique habits are often doubly terminated. Crystal types include trapezohedral, octahedral, cubic, or dodecahedral, and these usually have complex or rounded faces. Individual crystals are usually microscopic, although larger crystals are still known. Also in crusty crystalline masses with stalactitic cores.

Other ID Marks

1) Has a pungent, astringent taste.2) Highly soluble in water.

Striking Features

Mode of occurrence and taste.

Environment

In volcanic fumarole deposits of fresh eruptions, where rainfall that would have melted the crystals had not yet occurred. Also in underground burning coal seams in lignite deposits.

Varieties

✓ common  · ✗ uncommon

Uses

Naturally occurring Sal ammoniac crystals are uncommon and make unusual collector minerals, especially when interestingly formed in skeletal or snowflake-like crystal masses. Sal ammoniac is easily produced synthetically, and has many uses, especially as a cleaning agent in several industrial processes. It is used in the production of stained-glass windows, in making jewelry and metallic alloys, in photography, and in battery production. It is also used in production of food, including salty licorice.

Noteworthy Localities

The best-known examples of Sal ammoniac, with their typical skeletal or dendritic growths, are from Ravat, in the Tien Shan Mountains, Tajikistan.
Sal ammoniac was first described at Monte Somma, at Mount Vesuvius, Campania, Italy, where it formed from fumarole activity on this famous volcano. Another important Italian volcanic locality is the La Fossa Crater, on Vulcano Island, Italy. Other significant European localities include the São Pedro da Cova Mine, Gondomar, Portugal; and the Kladno Mine, Libušin, Bohemia, Czech Republic. In Mexico, Sal ammoniac has been found at the Paricutin volcano, Michoacan, Mexico. An interesting occurrence was the Huron River shale fire, Huron Co., Ohio, which formed complex microcrystals of Sal ammoniac.

Common Mineral Associations

Photos

Crystal forms

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Rounded Trapezohedron
Complex Trapezohedral
Radiating Crystal off Central Core