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

2. 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

3. 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

4. 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

5. 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

6. Sulfide Formulas continued
X can be
Sulfur
Selenium
Tellurium
Arsenic
Antimony

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

8. 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

9. 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

10. Anion Size Versus Coordination NumberIV 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

11. 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

12. 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

13. 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

14. 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

15. 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

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

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