Smithsonite is a mineral with a hardness of 5 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of zinc carbonate, their full chemical compound being ZnCO3.
Smithsonite is a mineral in the group of Nitrates, Carbonates, Borates, with a hexagonal crystal system.
It appears uncommonly in rhombohedral or scalenohedral crystals. But most of the time it appears with curved faces, like a thick creamy aqua-green mixture poured on rock and left to aggregate in clusters shaped like bunches of grapes, rounded, kidney-like, or to form like elegant icicles, and all of these are porous and concretionary.
It is a typical allochromatic mineral, which in its pure state is white, especially the kidney-shaped varieties, but becomes pale blue or green when copper impurities (probably malachite) are present; turning bright yellow with cadmium, pink or violet with cobalt or manganese and brown with tiny particles of iron hydroxides.
It is hard, heavy, fragile, with perfect rhombohedral cleavage, though this is rarely seen, because in masses the shell-like conchoidal fracture is common. It is translucent with vitreous to greasy luster. Many varieties show pinkish fluorescence if exposed to ultraviolet light. It is infusible, and is soluble in cold hydrochloric acid, giving off carbon dioxide.
Smithsonite occurs as a typical sedimentary precipitate produced by the action of waters rich in zinc sulfate on carbonate rocks. It is characteristically found in the oxidation zone of sulfide deposits (zinc, lead, and copper), and is generally associated with hemimorphite, cerussite, malachite, anglesite, pyromorphite, etc.
Small, colorless, rhombohedral crystals have been found in the famous mining area of Tsumeb (Namibia) and Broken Hill (Zambia). Blue-green clustered masses at Magdalena and Kelly, New Mexico (USA), Santander (Spain), and Lavrion (Greece). The classical slags at Lavrion provide attractive translucent gem-quality material.
Stalactitic yellow masses have been found at Marion, Arkansas (USA) and in Sardinia (mainly at Masua, near Iglesias, and at Monteponi). Masses and crusts of various colors were found in Italy in the Bergamo deposits (Gorno and Valle del Riso) and the Alps (Raibi, Udine). Sizable masses are worked commercially at Leadville, Colorado (USA), in Kazakhstan, and Turkey.
Varieties of smithsonite include:
Azulite – a translucent, pale blue variety of smithsonite found in Greece and Arizona, USA.
Turkey-fat ore – the yellow variety of smithsonite containing cadmium.
Aztec stone – a local term for greenish smithsonite.
Dry-bone ore – a term applied to an earthy, crumbly, honeycombed variety of smithsonite. This term is also employed sometimes to describe hemimorphite.
Herrerite – a blue and green copper-stained variety of smithsonite.
Santander – a local term for translucent, banded, bluish-green smithsonite from Spain.
Sardinia – a variety of smithsonite occuring on the coast of the island of Sardinia, Italy.
Misleading terms include:
azurite – a commercially misleading term for blue smithsonite.
bonamite – a misleading, commercial term for an apple-green, gem variety of smithsonite, resembling chrysoprase in color. Found in Kelly, New Mexico, USA. Frequently used as a jade imitation.
sacred turquoise – a misleading term for light blue variety of smithsonite.
Smithsonite can be confused with chrysoprase, hemimorphite, jade, and turquoise.
Smithsonite is named after James Smithson, the adventurous and nomadic British mineralogist and chemist, who, among vast range of interests, studied the uses of this stone in the making of brass. Though he never visited the United States, heleft a bequest in his will which founded the world-famous Smithsonian Institution in Washington, D.C.
Zinc is extracted from smithsonite.
When it shows good translucent green coloring or attractive banding, it is polished and used as an ornamental stone. Yellow-colored stones are rarely faceted and massive forms are cut into cabochons.
Smithsonite used to be called calamine, but this name is now used for a pink powder mixed in lotions and ointments applied on the skin to relieve itching and other minor irritations, even from poisonous plants, or as an astringent to dry out acne sores. This powder is a mixture of smithsonite and zinc silicates.
It is of interest to collectors and scientists concerned with the study of mineral deposits.