Minerals: Sulfides

Minerals are defined by five criteria: 1. Naturally Occurring, 2. Inorganic, 3. Solid, 4. Defined Chemical (Atomic) Formula, and 5. A unique set of physical properties.

Sulfides – are chemical compounds in which sulfur has combined with metallic and semi-metallic elements. Sulfides are very important ores of lead, zinc, iron, and copper. They form in hydrothermal veins below the water table as they are easily oxidizedto sulfates.

Specimen: Galena

Classification: Sulfide

Chemical Composition: PbS

Crystal structure: Cubic

Hardness: 2.5

Specific Gravity: 7.58

Luster: Metallic

Cleavage: Perfect cube

Fracture: Subconchoidal

Source: Forms in hydrothermal veins. Often occures with quartz, sphalerite, calcite, pyrite, and flourite.

Uses: Lead ore

Specimen: Pyrrhotite

Classification: Sulfide

Chemical Composition: Fe_1−xS (x = 0 to 0.2)

Crystal structure: Monoclinic

Hardness: 3.5 to 4.5

Specific Gravity: 4.53 to 4.77

Luster: Metallic

Cleavage: None

Fracture: Subconchoidal to uneven

Source: Commonly forms in magnetic igneous deposits, particularly basic/mafic or ultrabasic/ultramafic.

Uses: Collected

Specimen: Pyrite cluster

Classification: Sulfide

Chemical Composition: FeS₂

Crystal structure: Cubic

Hardness: 6 to 6.5

Specific Gravity: 5.0

Luster: Metallic

Cleavage: Indistinct

Fracture: Conchoidal to even

Source: Forms in hydrothermal veins and can be found  in igenous, sedimentary, and metamorphic rocks.

Uses: Source of sulphur dioxide and sulphuric acid.

Specimen: Pentameral pyrite crystal

Classification: Sulfide

Chemical Composition: FeS₂

Crystal structure: Cubic

Hardness: 6 to 6.5

Specific Gravity: 5.0

Luster: Metallic

Cleavage: Indistinct

Fracture: Conchoidal to even

Source: Forms in hydrothermal veins and can be found  in igenous, sedimentary, and metamorphic rocks.

Uses: Source of sulphur dioxide and sulphuric acid.

Specimen: Chalcopyrite

Classification: Sulfide

Chemical Composition: CuFeS₂

Crystal structure: Tetragonal

Hardness: 3.5 to 4

Specific Gravity: 4.3 to 4.4

Luster: Metallic

Cleavage: Poor

Fracture: Uneven to Chonchoidal

Source: Commonly forms sulfide ore deposits and hydrothermal veins.

Uses: Copper ore

Specimen: Sphalerite “blende” or “black jack”

Classification: Sulfide

Chemical Composition: (Zn,Fe)S

Crystal structure: Cubic

Hardness: 3.5 to 4

Specific Gravity: 3.9 to 4.1

Luster: Metallic

Cleavage: Perfect

Fracture: Chonchoidal

Source: Commonly forms in hydrothermal veins. Commonly found with quartz, galena, pyrite, dolomite, calcite, and barite. 

Uses: Industrial uses brass and batteries

Specimen: Sphalerite cluster on matrix

Classification: Sulfide

Chemical Composition: (Zn,Fe)S

Crystal structure: Cubic

Hardness: 3.5 to 4

Specific Gravity: 3.9 to 4.1

Luster: Metallic

Cleavage: Perfect

Fracture: Chonchoidal

Source: Commonly forms in hydrothermal veins. Commonly found with quartz, galena, pyrite, dolomite, calcite, and barite.

Uses: Industrial uses brass and batteries

Specimen: Realgar “ruby sulphur” “ruby of arsenic”

Classification: Sulfide

Chemical Composition: As₄S₄ or AsS

Crystal structure: Monoclinic

Hardness: 1.5 to 2

Specific Gravity: 3.56

Luster: Resinous to greasy

Cleavage: Good

Fracture: Conchoidal

Source: Commonly forms in low  hydrothermal veins and around hot springs.

Uses: Historically fireworks before powdered metals.

Specimen: Molybdenite

Classification: Sulfide

Chemical Composition: MoS₂

Crystal structure: Trigonal/Hexagonal

Hardness: 1 to 1.5

Specific Gravity: 4.62 to 5.06

Luster: Metallic

Cleavage: Perfect basal

Fracture: Uneven

Source: Forms in hydrothermal veins and granitic rocks.

Uses: Ore of molybdenum, an iron alloy

Data: Pellant, Chris. Smithsonian Handbooks: Rocks and Minerals, The clearest recognition guides avaiable. A Dorling Kindersley Book.