1 native elements, sulfides, and sulfosalts gly 4200 lab 2 - fall, 2014
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Native Elements, Sulfides, and Sulfosalts
GLY 4200
Lab 2 - Fall, 2014
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Native Elements
• The native elements may be divided into metallic, non-metallic, and semi-metallic
• Native elements are composed of a single element, uncombined with other elements
• They are often ores, especially the metallic native elements Gold, Silver, Copper, Platinum
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Native Element Luster
• The luster shows distinctive changes from one group to another Metallic group – metallic to dull metallic Semi-metal group – submetallic to dull metallic Non-metallic – various non-metallic lusters
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Sulfides
• A sulfide is a compound between sulfur, or another sulfur group element, and a metallic element
• Most of these minerals are opaque, and they often have characteristic colors, as well as distinctive streak colors
• A few are transparent to translucent – examples cinnabar, realgar, and orpiment
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Sulfide Formulas
• The general formula is AmXn where A represents metallic elements, X represents a sulfide group element whose oxidation state is -2, and m and n are integers
• The X anions are usually in the negative two oxidation state Exception: Minerals with the S2 dimer, such as
pyrite, marcasite, and arsenopyrite
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Sulfide Formulas continued
• X can be Sulfur Selenium Tellurium Arsenic Antimony
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Position in Periodic Table
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Other Oxidation States
• All of the sulfide group elements occur in other oxidation states, for example As5+ forms arsenates
• But in the 2- state they belong to the sulfide group
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Anion Size
• All of the sulfide group anions are large
• The large anionic size tends to favor coordination with large cations As a result sulfide minerals are very often
important economic minerals (ores) because they associate with the relatively rare larger cations
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Anion Size Versus Coordination Number
Anion IV VI VIII
O2- O.130 0.132 0.134
S2- 0.156 0.172 0.178
Se2- 0.188 ______ 0.190
All sizes are in nanometers
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Sulfide Ores• Major sulfide ore minerals include:
Mineral Element
Galena Lead
Sphalerite Zinc
Chalcopyrite, Chalcocite, Bornite, Covellite
Copper
Greenockite Cadmium
Argentite Silver
Pentlandite, Niccoline, Millerite Nickel
Cinnabar Mercury
Stibnite Antimony
Arsenopyrite Arsenic
Molybdenite Molybdenum
Cobaltite Cobalt
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Solid Solution
• The sulfides are also characterized by extensive solid solutions
• Many of the cations are of similar size and charge and they can substitute extensively
• Anionic substitution also occurs• The physical characteristics of solid
solutions will be between their end-member minerals
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Solid Solution Example
• Galena is PbS, the only ore of lead
• Galena is found with inclusions of other elements Ag, Zn, Cd, Sb, As & Bi
• Se can substitute for S and forms a complete solid solution series
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Sulfide Characteristics
• Many sulfide minerals have resonant bonding, with a partial metallic characteristic Results in metallic to dull metallic luster
• SG is often high, because of the presence of metallic elements, and sometimes heavy anions like Se or Te
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Sulfide Hardness
• Most sulfide group minerals are soft to soft-moderate hardness Exception: Sulfides with the S2 dimer, such as
pyrite, marcasite, and arsenopyrite, are moderately hard
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Sulfosalts
• This term signifies a mineral in which a semi metallic element replaces the metals Examples: enargite, tetrahedrite
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Text Reference
• See chapter 15 in the text for more information on native elements, sulfides, and sulfosalts, pp. 331-367
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