Introduction to MineralogyDr. Tark Hamilton

Chapter 4: Lecture 13The Chemical Basis of Minerals

(Parsimony & Isostructural Minerals)

Camosun College GEOS 250

Lectures: 9:30-10:20 M T Th F300

Lab: 9:30-12:20 W F300

#5 - Principle of Parsimony

• # of contrasting elements are small because there are few anion or cation sites

• Complex compositions tend toward several constituents (cations) in the same kind of site

• This is termed solid solution: Fe for Mg, Si for Al, Ca for Na (definite not exact compositions)

• Goldschmidt’s rules say ions have to be similar size +/-15% and +/- 1 charge unit

Limited Types of Coordination

Octahedral – Na & Cl

Octahedral – CaTetrahedral – F

Octahedral – emptyTetrahedral - S

Halite

Fluorite

Sphalerite

Halite: Hesse, Germany S. Menig 2005, Saskatchewan Rob Levinsky

4/m 3 2/mHexoctahedral

CubesCubic cleavage on (001)

Evaporite deposits,Salt domes

Bedded sediments

Halite named byJ.D. Dana for

Greek αλς “sea”

Muhlhausen Alsace, France John Betts 2002; Christopher O’Neill

Fluorite: Rogerly Mine, Weardale, Durham Co. Pennines Wales, Jesse Fisher 2001

4/m 3 2/mHexoctahedral

Cubes with Penetration twins (111)

Cleavage octahedral

The term fluorescence isderived from fluorite,

which will often exhibit this effect when Y & CeSubstitute for Ca ions

Ore of FluorineProduction of HF

Flux in Steel & Glass

Greisens, GranitesPegmatites & Gangue

in Hi T Pb-Zn ores

OctahedraCatamarca Argentina

J.C. Lodovici

TetrahexahedronNilaw-KolumAfghanistan

Fabre Minerals

Mineral Names - Trivial Pursuits!

Halite – Greek, halos for salt, mineral of health

Fluorite – Latin fleure to flow, melts easily, flux

Sphalerite – Greek treacherous, zincblende,German “blind”, decieving,rubyzinc or blackjack

Sphalerite: 43m Hextetrahedral

v.Marmatite Elmwood Mine TN, John Betts 2003

var. Ruby-blende, Taz. Aus.R. Bottrill 2006

CdS Greenockite coating, Tazmania, viccloete

Sphalerite

• Think about those empty octahedra of Zn!• X3 to x10 thermal and electrical conductivity

compared to other sulphides• With Fe substitution, darkens (blackjack), reflects

more & enhances magnetic susceptibility• w/ Pyrrhotite Fe1-xS, Fe-Zn a geothermometer,• Main ore of Cd, isostructural w/Greenockite CdS

• alters to Goslarite ZnSO3 or Smithsonite ZnCO3

Parsimony - Complex compositions tend toward several constituents (cations) in the same

kind of site

• Monoclinic Amphiboles:

• Hornblende, Richterite, Actinolite, Tremolite, Glaucophane, Riebeckite

• (Ca,Na)2-3(Mg,Fe,Al)5Si6(Si,Al)2O22(OH)2

• For chemical calculations sometimes O23

Amphibole Polyhedral SitesProjected along a - axis

J.J Papike, 1969

Si+4 , Al+3Mg Fe, Mn

Al+3 , Fe+3 Ti+4

Ca+2 , Na+

Ca+2 , K+

T2

Riebeckite:[ ][Na 2][Fe2+3Fe3+

2][(OH)2][Si8O22]Golden Horn Batholith, Washington Pass, ROM

Richterite: Na[CaNa][Mg5][(OH)2][Si8O22]Mt. Ngongotaha Rotorua NZ

Magnesiohornblende:[Ca2][Mg4Al][(OH)2][AlSi7O22]

Eifel Mtns Rhineland GermanyJ. Weissmann 2008

Chromian Tremolite:[Ca2][Mg5][(OH)2][Si8O22]

Haliburton ONJohn Betts 2001

Isostructural Minerals

• UO2 & CaF2 (Uraninite & Fluorite, Oct/Tet) (different in solutions, Linear & Oct/Cubic, different energy or they wouldn’t dissolve!)

• NaCl Halite & MgO Periclase & PbS Galena & MnS Alabandite & AgCl Chlorargyrite & TiN Osbornite (named after Donny & Marie?)

• Stishovite SiO2 & Rutile TiO2 are both octahedral, for Silicon this takes GPa’s of P

• Isostructural Groups: Barite (sulphates), Calcite (Carbonates) Aragonite (Carbonates)

Uraninite & GummiteGreat Bear Lake, NWT

M Arliguie

UO2

Haliburton ONJohn Betts 2001

Uraninite radiation damage halo

Parfurbwirt, AustriaChris Auer, 1984