Native Elements, Sulfides, and Sulfosalts GLY 4200 Lab 2 - Fall, 2018

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

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

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

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

Sulfide Formulas continued X can be Sulfur Selenium Tellurium Arsenic Antimony

Position in Periodic Table S, Se, and Te are in the lower part of column 16 As and Sb are in column 15

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

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

Anion Size Versus Coordination Number 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

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

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

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

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

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

Sulfosalts This term signifies a mineral in which a semi metallic element replaces the metals Examples: enargite, tetrahedrite

Text Reference See chapter 15 in the text for more information on native elements, sulfides, and sulfosalts, pp. 331-367