Sulfides as Gems?

by Kevin Barnett

Table of Contents

Introduction Galena
Sphalerite Chalcopyrite
Pyrite Marcasite
References

Introduction

    This page has been put together by a college student in a Gemstones and Gemology course taught at Emporia State University.  It was designed to inform and expand your knowledge on sulfides. I hope you find this page interesting and informative.

    Sulfides are minerals that conbine metallic cations (+) with a sulfur anion (S-) This is an important class of minerals because it includes the majority of the ore minerals.  Most of these minerals are opaque with distinctive colors and streaks (Encyclopedia of Mineralogy).

    Native elements and sulfides can both contain polymorphic minerals. Polymorphism is the ability of a specific chemical substance to crystallize in more than one configuration, which is dependent upon changes in temperature, pressure, or both.  One type of polymorphism is reconstructive and examples include diamond/graphite and pyrite/marcasite.  The carbon minerals, diamond/graphite, are distinct enough that identification is not a problem. The sulfides, pyrite/marcasite, are very similar in appearance and difficult to distinguish in hand specimen although they do have different crystal systems and can vary in habit (Encyclopedia of Minerals).

Galena
    Physical properties:
        Chemical composition: lead sulfide (PbS)
        Hardness: 2.5
        Specific gravity: 7.4- 7.6
        Luster: bright metallic
        Color/streak: metal gray/lead gray
        Cleavage/fracture: good cleavage in two directions/subconchoidal
        Crystal system: isometric
        Crystal form: cubic or octohedron
        Tenacity: brittle
        Geological/Geographical occurrence: geologically galena is found in hydrothermal veins, associated with other sulfide minerals.  Some of the main geographical locations for this mineral are:  Freiberg, Saxony Germany; Czech and Slovak Republics; British Columbia, Canada; Australia.

    The softness of galena allows it to be manipulated easily into jewelry pieces.  Galena can be used in wire wrapping for gems with low hardness, so the material does not scratch the gemstone (The Mineral and Gemstone Kingdom).


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The Mineral and Gemstone Kingdom

Table of Contents
Sphalerite
    Physical properties:
        Chemical composition: zinc sulfide (ZnS)
        Hardness: 3.5 to 4
        Specific gravity: 3.9 to 4.1
        Luster: resinous to adamantine
        Color/Streak: colorless when pure, brown, red, orange, and yellow/white, yellowish brown
        Cleavage/Fracture: good in one direction/conchoidal
        Crystal system: isometric
        Crystal form: tetrahedral, and octahedral
        Tenacity: brittle
        Geological/Geographical occurrence: found with Zinc elements similar to galena, also found in hydrothermal veins with pyrite and magnetite.  Some geographical occurrence for this mineral are as follow: the Tri-State area of Kansas, Missouri, and Arkansas, in the U.S.; Canada; Australia; Poland; Mexico; and Japan.

Sphalerite is an important mineral to collectors, and some transparent varieties are occasionally faceted for collectors (The Mineral and Gemstone Kingdom).


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The Mineral and Gemstone Kingdom
Table of Contents

Pyrite
    Physical properties:
        Chemical composition:  Iron Sulfide (FeS2)
        Hardness: 6 to 6.5
        Specific gravity: 5.02
        Luster: metallic or splendent
        Color/Streak: brass-yellow tarnish/greenish or brownish-black
        Cleavage/Fracture: none/ conchoidal
        Crystal System: isometric
        Crystal Form: pyritohedron
        Tenacity: brittle
        Geological/Geographical occurrence: found in sedimintary rocks around or in hydrothermal veins/In the U.S., there are also many fine localities. In Park City, Bingham Co., Utah, very large, well shaped pyritohedrons and pyrite cubes have been found, as well as in the American Mine in the Bingham Canyon, Salt Lake Co., Utah. Large, intergrown cubes, many times partially octahedral, occur in abundance at Leadville, Lake Co., Colorado. Pyrite "Dollars" are mostly found in Sparta, Randolph Co., Illinois. The French Creek Mine in Chester Co., Pennsylvania is famous for the octahedral crystals that occur there, although most are distorted. Many interesting nodules were recently discovered in Alden, Monroe Co., New York

Pyrite was polished by the Native Americans in the early times and used as mirrors. Today, it is used as an ornamental stone, as well as a very popular stone for the amateur collector. It is sometimes used as gemstone by being faceted and polished for use as a side jewel in a ring, necklace, or bracelet. Pyrite is many times wrongly called "Marcasite" in the gem trade (The Mineral and Gemstone Kingdom).


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The Mineral and Gemstone Kingdom

Table of Contents
Chalcopyrite
    Physical properties:
        Chemical composition:  Copper Iron sulfide (CuFeS2)
        Hardness: 3.5 to 4
        Specific gravity: 4.1 to 4.3
        Luster: metallic
        Color/Streak: brassy-yellow tarnishes blue, purple, and red/ greenish-black
        Cleavage/Fracture: none/ uneven
        Crystal System: tetragonal
        Crystal Form: tetrahedrons and octahedrons
        Tenacity: brittle
        Geological/Geographical occurrence:  found in or around hydrothermal veins, replacement deposits of copper and metal minerals.  Chalcopyrite is a fairly common mineral, and therefore only the finest of localities will be mentioned. Large, well shaped crystals occur in numerous places in Cornwall, England, as well as Akita, Ugo, and Tochigi Perfectures, Japan. Many fine crystals occur in the northern section of Mexico; certain occurrences are La Bufa, Chihuahua; Charcas, San Luis Potosi; and the Noche Buena mine, near Mazapil, Zacatecas.

Chalcopyrite is sometimes polished into beads and pendants as cheap jewelry (The Mineral and Gemstone Kingdom).


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The Mineral and Gemstone Kingdom
Table of Contents

Marcasite
    Physical properties:
        Chemical composition: iron sulfide (FeS2)
        Hardness: 6 to 6.5
        Specific gravity: 4.89
        Luster: metallic
        Color/Streak: pale-bronze yellow tarnishes brown/ grayish-black
        Cleavage/Fracture: good in two directions/ conchoidal
        Crystal System: orthrhombic
        Crystal Form: bipyramidal and tabular
        Tenacity: brittle
        Geological/Geographical occurrence: found in metalliferous veins, lead and zinc ores, and hydrothermal veins.  Marcasite is found, usually associated with Galena, Sphalerite an Dolomite in Joplin, Jasper Co., Missouri, and the surrounding area. Coxcomb aggregates and elongated crystals have been found there. Guanajuato, Mexico, has also provided many fine crystals.

Pyrite used as a gem is improperly termed marcasite. This is wholly incorrect, as marcasite is never used as a gem (The Mineral and Gemstone Kingdom). Marcasite is frequently has been mounted as a marquise ring, therefore it has sometimes been misspelled marquisite.  It has been set in white-metal setting or a pave setting or cut cabochon or as flattened rose cut with flat back.

Image is courtesy of
The Mineral and Gemstone Kingdom


Photo date 2/02,
© by Berg and Dougan.
This image was taken from the Gemstones and Gemology and shows pyrite used as jewelry.  This particular piece of jewelry is called marcasite jewelry, but made with pyrite.

Table of Contents

References

  • Frye, K. (Ed.). Encyclopedia of mineralogy. Stroudsburg, PA: Hutchinson Ross Publishing Co.
  • Roberts,W.L., Rapp, Jr., G.R., & Weber, J. (1974). Encyclopedia of minerals. NY: Van Nostrand Reinhold Publishing Co.
  • The Mineral and Gemstone Kingdom. (Retrieved April 24, 2002). Sulfides. World Wide Web URL: http://www.minerals.net/mineral/sort-met.hod/group/group1.htm
  • Manuthehr-Danai,M. Dictionary of Gems and Gemology. (2000) Springer-Verlag Berlin, Germany: Heidelberg New York.

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