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The Mineral smithsonite

Globular Yellow Smithsonite

Smithsonite occurs in a wide variation of colors. Its typical globular habit and often vibrant colors make this a desirable mineral for collectors. Smithsonite is composed of zinc carbonate, but the zinc may be partially replaced with other elements. Those elements are responsible for the color variations. For example, copper  often causes green or bright blue colors, and cobalt causes a pink to purple color. Cadmium makes Smithsonite yellow, and iron gives it a brown to reddish-brown color.


Smithsonite rarely occurs in visible crystals. The only two locations to produce large crystals of significance are Tsumeb, Namibia; and the Kabwe Mine (Broken Hill), Zambia. Virtually all other findings of this mineral are in globular or botryoidal-like forms. Many of the rounded forms have a very distinct feathery or sparkling light effect. Botryoidal Smithsonite aggregates are sometimes lubricated with oils by dealers to enhance luster and appeal to collectors.

Smithsonite belongs to the calcite group of minerals, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a solid solution series. All members of the calcite group crystallize in the trigonal system, have perfect rhombohedral cleavage, and exhibit strong double refraction in transparent rhombohedrons. 
 
 Smithsonite is named in honor of James Smithson, the founder of the Smithsonian Institution.

Chemical Formula

ZnCO3

Color

Blue, green, yellow, yellow-green, orange-yellow, pink, purple, gray, brown, white, and colorless. May contain multicolored color zoning patterns and banding.

Crystal System

Hexagonal

Properties

Streak
White
Hardness
4 - 5
Transparency
Translucent to nearly opaque
Specific Gravity
4.3 - 4.5
Luster
Vitreous, greasy, pearly, dull
Cleavage
1,3 - rhombohedral, usually curving
Fracture
Uneven, splintery. Conchoidal in individual crystals.
Tenacity
Brittle
Other ID Marks
1) May fluoresce pink in shortwave ultraviolet light.
2) Clear, transparent, rhombohedral crystals exhibit strong double refraction.

Crystal Habits

Mainly globular, botryoidal, stalactitic, and concretionary. Occasionally occurs as lenticular lumps, encrusting, massive, grainy, and as banded formations. Masses are sometimes porous. Crystals are rhombohedral and scalenohedral, and usually are rounded with curved faces. Crystals may contain triangular growth patterns.

Smithsonite is also known to form pseudomorphs of other minerals such as Calcite, Galena, and Fluorite, assuming the crystal shapes of those minerals.

3D Crystal Atlas

Additional Information

Composition
Zinc carbonate, usually with some iron, magnesium, and calcium, occasionally with some cadmium, copper, and cobalt.
In Group
Carbonates; Calcite Group
Striking Features
High hardness for a carbonate and interesting crystal habits
Environment
As a secondary mineral formed from the alteration of primary zinc minerals in the oxidation zone.
Rock Type
Metamorphic

Other Names

Calamine Calamine was the original name of the mineral Hemimorphite, and described this zinc ore in globular and botryoidal forms. The mineral Smithsonite, which closely resembles Hemimorphite and is also a zinc ore, was also called Calamine by the miners and early collectors. Today use of this term has been discouraged because of its confusion of mineral species.

Varieties

 -   Blue or green globular Smithsonite with a pearly luster. This term is usually used to describe Smithsonite in the gem trade.
 -   Yellow or yellow-green Smithsonite colored by cadmium impurities.
 -   Blue to green Smithsonite colored by copper impurities.
 -   Describes the massive, porous, and dull variety of Smithsonite, which often assumes a honeycomb shape.
 -   Describes globular, botryoidal, and stalactitic forms of yellow Smithsonite.

Uses

Smithsonite is an ore of zinc. It is sometimes polished and used as an ornamental stone, which is known as Bonamite in the gem trade. It is a minor gemstone.

Noteworthy Localities

Large Smithsonite crusts are found in a number of areas on the island of Sardinia, Italy, particularly at the Massua and Monteponi Mines, in Iglesias. Blue-green botryoidal masses and crusts are common at the mines at Lavrion, Greece. 

Individual Smithsonite crystals and crystal clusters of all colors are well-known from Tsumeb, Namibia. Two other African localities which provided visible crystals of this mineral are Berg Aukas, Grootfontein, Namibia; and the Kabwe Mine (Broken Hill), Zambia. The famous Australian locality of Broken Hill, New South Wales, is known for its abundance of minerals including Smithsonite.

Mexico has two outstanding Smithsonite localities which contain beautifully colored Smithsonite, including deep pink and electric green colors. These are the Refugio Mine, Choix, Sinaloa; and the San Antonio Mine, Santa Eulalia District, Chihuahua.

The U.S. has many fine Smithsonite occurrences; perhaps the most famous being the Kelly Mine, Magdalena, Socorro Co., New Mexico. The No. 79 Mine, Hayden, Gila Co., Arizona is known for its dark and apple-green Smithsonite. Bright yellow and orange-yellow specimens have come from Rush, near Yellville, Marion Co., Arkansas. A large industrial zinc deposit produced Smithsonite in Leadville, Lake Co., Colorado. Other localities are Cerro Gordo, Inyo Co., California; the Hidden Treasure Mine, Ophir Hill, Tooele Co., Utah; and Mineral Point, Iowa Co., Wisconsin.

Distingushing Similar Minerals

Hemimorphite  - Lighter in weight (2.4 - 3.5), otherwise very difficult to distinguish.
Prehnite - Harder (6 - 6½), doesn't effervesce in hydrochloric acid.
Wavellite - Softer (3½ - 4), lighter in weight, doesn't effervesce at al
Calcite - Softer (3), strongly effervesces in hydrochloric acid, even if acid is cold and diluted.
Chrysocolla - Softer, usually has a deeper color. Otherwise difficult to distinguish.

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