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Globular Yellow Smithsonite

The Mineral smithsonite




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 rarely occurs in visible crystals. The only two locations to produce large crystals of significance are Tsumeb, Namibia, and Broken Hill, Zambia. Virtually all other findings of this mineral are in globular or botryoidal-like forms. Many of the rounded forms have a feathery or sparkling light effect.

Smithsonite is essentially zinc carbonate, but the zinc may be partially replaced with other elements. This is responsible for the color variations this mineral exhibits. Copper is responsible for green to blue coloring, and cobalt causes a pink to purple color. Cadmium makes Smithsonite yellow, and iron gives it a brown to reddish-brown color.
 
Botryoidal Smithsonite aggregates are occasionally lubricated with oils to enhance luster and appeal to collectors. Smithsonite is named in honor of James Smithson, the founder of the Smithsonian Institution.
Chemical Formula ZnCO3
Composition Zinc carbonate, usually with some iron, magnesium, and calcium, occasionally with some cadmium, copper, and cobalt.
Variable Formula (Zn,Fe,Mg,Ca,Cd,Cu,Co)CO3
Color Blue, green, yellow, yellow-green, orange-yellow, pink, purple, gray, brown, white, and colorless. May contain multicolored color zoning patterns and banding.
Streak White
Hardness 4 - 5
Crystal System Hexagonal
3D Crystal Atlas
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Crystal Forms
and Aggregates
Mainly occurs globular, botryoidal, stalactitic, and concretionary. Occasionally occurs as lenticular lumps, encrusting, massive, grainy, and as banded lumps. Masses are sometimes porous. Crystals, which are rare, 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.
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 a strong double refraction.
Complex Tests Effervesces in hydrochloric acid
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
Popularity (1-4) 2
Prevalence (1-3) 2
Demand (1-3) 2

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

Mexico has two outstanding 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 occurrences; perhaps the most famous being the Kelly Mine, Magdalena, Socorro Co., New Mexico. The No. 79 Mine, Hayden, Gila Co., Arizona is famous 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 is 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.

COMMON MINERAL ASSOCIATIONS
Azurite, Malachite, Cerussite, Hemimorphite, Aurichalcite, Anglesite, Pyromorphite, Hydrozincite, Galena

DISTINGUISHING 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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