The mineral smithsonite

Chemical Formula

ZnCO₃

Composition

Zinc carbonate, usually with some iron, magnesium, and calcium, occasionally with some cadmium, copper, and cobalt. Combinations of all these elements do not exist; only particular combinations can exist. Nevertheless, the variable elements are all listed together in the "Variable Formula" field to avoid confusion. (See the Brownspar Group for more information.)

Variable Formula

(Zn,Fe,Mg,Ca,Cd,Cu,Co)CO₃

Color

White, colorless, blue, green, yellow, yellow-green, orange-yellow, pink, purple, gray, brown; sometimes with color zoning patterns and banding

Streak

White

Hardness

4 - 5

Crystal Forms
and Aggregates

(Hexagonal) Crystals (rhombohedral and scalenohedral) are rounded and have curved faces. Otherwise occurs globular, stalactitic, and concretionary. Occasionally occurs as lenticular lumps, encrusting, massive, grainy, and as banded lumps. Masses are sometimes porous.

Transparency

Translucent to nearly opaque

Specific Gravity

4.3 - 4.5

Luster

Vitreous to subadamantine; greasy, pearly, dull

Cleavage

1,3 - rhombohedral, usually curving

Fracture

Uneven, splintery. Conchoidal in individual crystals.

Tenacity

Brittle

Other ID Marks

1) Sometimes fluorescent pink in shortwave ultraviolet light
2) Clear, transparent, rhombohedral crystals exhibit a strong double refraction

Other Names

Calamine was the name of the mineral Hemimorphite before it was found in individual crystals, when it only occurred in globular masses. Smithsonite, which resembles Hemimorphite, was also frequently called Calamine. This led to great confusion differentiating two minerals identical in appearance. Therefore, all countries and mineral organizations have agreed to drop the name Calamine and only use the scientifically correct names of Hemimorphite and Smithsonite. Nevertheless, the name Calamine is still seen, especially in European countries.

Varieties

Bonamite - Blue or green globular Smithsonite with a feathery luster. Usually used to describe Smithsonite in the gem trade.

Dry Bone Ore - Massive, porous, dull variety of Smithsonite, usually assuming a honeycomb shape.

Turkey Fat Ore - Globular and stalactitic masses of yellow Smithsonite.

Cadmium Smithsonite - Yellow or yellow-green Smithsonite colored by cadmium impurities.

Copper Smithsonite - Blue, blue-green, or green Smithsonite colored by copper impurities.

In Group

Carbonates ; Calcite group

All About

Smithsonite belongs to the calcite group, 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 partial solid solution series. All members of the calcite group crystallize in the trigonal subdivision of the hexagonal system (as rhombohedrons and scalenohedrons), have perfect rhombohedral cleavage, and exhibit a strong double refraction in transparent rhombohedrons.

Smithsonite rarely occurs in visible crystals. Recently, two African mines have produced many large crystals different from all other Smithsonite specimens.

Smithsonite is essentially zinc carbonate, but the zinc is usually partially replaced with other elements. This is responsible for the great color variations this mineral exhibits. Copper is responsible for a green to blue coloring; cobalt, pink to purple; cadmium, yellow; iron, brown to reddish-brown. Smithsonite is a secondary mineral formed from the alteration of primary zinc minerals in the oxidization zone.

Smithsonite is named in honor of James Smithson, the founder of the Smithsonian Institution.

Uses

Smithsonite is an ore of zinc when it occurs in appreciable quantities. It is sometimes polished and used as an ornamental stone, where it is known as "Bonamite".

Striking Features

High hardness for a carbonate, common crystal habits

Complex Tests

Effervesces in hydrochloric acid

Popularity (1-4)

Prevalence (1-3)

Demand (1-3)

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
Calcite - softer (3), strongly effervesces in hydrochloric acid, even if acid is cold and diluted
Chrysocolla pseudomorph after Quartz - Quartz faces harder, Chrysocolla faces softer

Commonly
Occurs With

Azurite, Malachite, Cerussite, Hemimorphite, Aurichalcite, Anglesite, Pyromorphite, Hydrozincite, Galena

Noteworthy
Localities

Large yellow crusts are found in the island in a number of area on the island of Sardinia, Italy, particularly at Monteponi, Massua, and Iglesias. Blue-green botryoidal masses and crusts occur largely at Lavrion, Greece. Other European localities include Satander, Spain; St. Gotthard, Switzerland; Aachen, Germany; and Bleiberg, Austria. Also found in Cornwall and Cumbria, England and Ireland. Single individual crystals, usually colorless or very lightly tinted were found in Tsumeb, Namibia, and in the Broken Hill Mine in Zambia. Blue-green and pink and purple masses, sometimes banded, have come Barranca de Cabre, Mexico.
The U.S. includes many fine occurrences; perhaps the finest being Kelly and Magdalena, Socorro Co., New Mexico. Bright yellow and orange-yellow specimens have come from Yellville, Marion Co., Arkansas. A large industrial deposit worked for obtaining zinc is in Leadville, Lake Co., Colorado. Other localities are Cerro Gordo, Inyo Co., California; the Tintic District, Juab Co., Utah; Bisbee, Cochise Co., Arizona; the No. 79 Mine in Gila Co., Arizona; and Bamford, Lancaster Co., Pennsylvania. Small crystals embedded in Hemimorphite were recently discovered in Ogdensburg, Sussex Co., New Jersey.

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Links

Picture Links

1. Yellow Smithsonite ("Turkey Fat Ore")
2. Blue Smithsonite