Mineral

Presentation Transcript

Mineral/Crystal Chemistry and Classification of Minerals Revisited Coordination, Solid Solution, Polymorphs and Isomorphs, Mineral Classes

Mineral and Crystal Chemistry Minerals have: Characteristic geometric game plan or structure of constituent molecules that is consistent and rehashing in a 3-D game plan (CRYSTALLINE SOLID) Arrangement of iotas relies on upon their ionic span and valence Many minerals can be conceptualized as anions (or anion edifices) firmly pressed together with cations filling in the interceding spaces (COORDINATION POLYHEDRA) Fixed or settled scope of concoction creation (FORMULA) Substitution of one component for another (SOLID SOLUTION) Depends on their ionic range and valence Substitution might be finished or constrained, straightforward or coupled, and changes with P-T conditions

Ionic sweep (IR) and Valence Cations (+) — > for the most part littler IR Anions (- ) — > by and large bigger IR Variable dependant on nuclear number and connection with different particles Atomic Theory

The Coordination Principle: Geometry of Atomic Building Blocks In an ionically reinforced substance (all minerals for our motivations) cations are encompassed by anions (or anionic edifices) In stable mineral precious stones The number and course of action of anions encompassing a cation structures a Coordination polyhedron

The Coordination Principle Coordination polyhedron If all particles are a similar size, they can be stuffed together so that every iota touches 12 others (Hexagonal or Cubic nearest pressing)

The Coordination Principle Coordination polyhedron BUT iotas shift in size So the size and state of the coordination polyhedron is dictated by the ionic radii of the cation and (anion complex) included Radius proportion (cation range/anion span) This shape is depicted by the quantity of anions encompassing a cation: Coordination number (C.N.)

Coordination Polyhedron A. Triangular (CN = 3) B. Tetrahedral (CN 4) C. Octahedral (CN 6) D. Cubic (CN 8) E. Dodecahedral (CN 12)

The Coordination Principle Oxygen (O - 2 ) is the most widely recognized anion in coordination polyhedron Cations organize with oxygen in predicable ways (see Ch. 4, p. 10) Minerals have particular physical areas (locales) that can hold just a couple sorts of particles Each site has particular coordination polyhedron sort

The Coordination Principle Coordination clarifies anion bunches O is all the more firmly attached to focal, profoundly charged cation than to different cations Examples: C +4 in triangular coordination (CN = 3) produces (CO 3 ) - 2 S +6 in tetrahedral coordination (CN = 4) produces (SO 4 ) - 2 Si +4 in tetrahedral coordination (CN = 4) produces (SiO 4 ) - 4

Formula mirrors the extents of components (cations and anions) exhibit in the mineral Common traditions: Subscripts demonstrate nuclear extents; superscripts demonstrate charge Commas for either-or; ex: olivine [(Mg,Fe) 2 SiO 4 ] Anion buildings normally in enclosures; ex: dolomite [CaMg(CO 3 ) 2 ] Historically controlled by wet concoction strategies Modern procedures ordinarily utilize centered vitality bar (electron or particle microprobe) Reported at wt% of components or oxides Must be changed over to nuclear extents Mineral Formulas

Mineral Formulas: Recalculation Formula = CuFeS 2 Converts wt% of components or oxides into a mineral equation (unadulterated substance or strong arrangement) *Calculated by wt%/nuclear wt Ex for Cu: 34.30/63.54 = 0.5398 **Normalized to make the most modest number equal to 1

100% C 0% B 100% B 100% A 0% A 100% B 100% A Mineral Formulas: Graphical Representation Can indicate relative extents of components in a mineral In wt%, oxide wt%, or nuclear extents Especially valuable in indicating multi-segment frameworks and strong arrangement frameworks Three segments Two segments

Mineral Formulas: Graphical Representation Example: CaO – MgO – SiO 2 framework

Atomic Substitution/Solid Solution Homogeneous crystalline solids of variable synthetic piece Many minerals fluctuate in their organization Elements are promptly substituted (nuclear substitution) for each other in numerous precious stone structures, when certain conditions are met

Atomic Substitution/Solid Solution Requires: Valences of substituting particles are not any more not the same as 1 Na +1 for Ca +2 Al +3 for Si +4 Difference in the measure of substituting particles must be <15% (at room temperature)

Some substitutions include finish strong arrangement Involves particles of (about) equivalent charge and size Any creation (blend) may happen between end part sytheses Examples: Olivine arrangement: Forsterite (Mg 2 SiO 4 ) to Fayalite (Fe 2 SiO 4 ) Plagioclase feldspar arrangement: Albite (NaAlSi 3 O 8 ) to Anorthite (CaAl 2 Si 2 O 8 ) Atomic Substitution/Solid Solution

Some substitutions include incomplete or restricted strong arrangement Involve particles of various sizes or charges Limited arrangements (blends) may happen between end individuals Examples: Carbonates: Limited strong arrangement between Calcite (CaCO 3 ) to Dolomite [CaMg(CO 3 ) 2 ] and Magnesite (MgCO 3 ) to Dolomite Pyroxene assemble: Limited arrangement between Hypersthene (MgSiO 3 ) and Diopside (CaMgSi 2 O 6 ) Atomic Substitution/Solid Solution

Some substitutions are straightforward 1 for 1 substitution of particles of equivalent charge Some substitutions are coupled Substitution includes at least 2 particles Necessary to adjust diverse charges Examples: Carbonates: Simple strong arrangement between Magnesite (MgCO 3 ) and Siderite (FeCO 3 ) Plagioclase feldspar: Coupled arrangement between Albite (NaAlSi 3 O 8 ) to Anorthite (CaAl 2 Si 2 O 8 ) Atomic Substitution/Solid Solution

Atomic substitution is more noteworthy at higher temperature (gem grids are more open) and can oblige more prominent ionic span deviation (than 15%) Na +1 IR = 0.97 K +1 IR = 1.33 Ca +2 IR = 0.99 Solid Solution & T-P Controls Atomic substitution is more noteworthy at higher weight since it can change the measure of crystallographic destinations and particles, along these lines suit more prominent ionic range deviation

Pyrite, FeS 2 (Fe +2 S 2 ) , Cubic Marcasite, FeS 2 (Fe +2 S 2 ) , Orthorhombic Polymorphism a similar compound recipe applies to (at least two) unmistakable mineral species Chemical sythesis may not be adequate to assign a particular mineral animal varieties (physically homogeneous and detachable segment of a material framework) Polymorphs have distinctive gem shapes (nuclear courses of action) and distinctive physical properties Different polymorphs happen therefore of contrasting natural conditions, chiefly temperature and weight

Polymorphs Examples: Diamond and Graphite (C); Diamond Graphite Geobarometer: (decides weight of development)

Polymorphs Examples: Quartz, Tridymite, and Cristobolite (SiO 2 ); Tridymite Quartz Cristobalite

Polymorphs Example: Calcite and Aragonite (CaCO 3 ); Calcite Aragonite

Isomorphism (Isostructuralism) Minerals with practically equivalent to equations where the relative sizes of cations and anions are comparative and gem structure is indistinguishable or firmly related Typically (however not generally) the reason for gathering and characterization, e.g. Garnet bunch, Amphibole gather, Mica assemble, Pyroxene amass Galena, PbS Halite, NaCl

Isomorphism Anions and cations of isomorphic minerals have a similar relative size a similar coordination Crystallize in a similar precious stone structure Share likeness of gem structure however not (really) compound conduct Ex: Halite and Galena, PbS Halite, NaCl

Isomorphism Some isomorphic minerals share firmly related recipes and indistinguishable gem structures Ex: Aragonite (orthorhombic) and Calcite (trigonal) Groups

Some isomorphic minerals have such comparable organizations and structures that they shape strong arrangement Complete strong arrangement between Albite (NaAlSi 3 O 8 ) and Anorthite (CaAl 2 Si 2 O 8 ) Limited strong arrangement between Calcite (CaCO 3 ) and Magnesite (MgCO 3 ) Isomorphism and strong arrangement are unmistakable however related ideas Isomorphism and Solid Solution Some isomorphic minerals don't have strong arrangement; Ex: Halite (NaCl) and Galena (PbS) Some strong arrangements don't have isomorphic end individuals; Ex: Sphalerite (Zn, Fe)S (cubic) and Pyrrhotite Fe 1-x S (hexagonal) Sphalerite Pyrrhotite

Class (synthetic - anion complex) Subclass (nuclear structure) Group (concoction and basic) Species (singular mineral – name) Variety (particular variety) Hierarchy of Mineral Classification Class: Silicate (SiO 4-) Subclass: Tektosilicate (system) Group: Plagioclase Series (An-Ab) Species: Oligoclase (70-90% Ab) Variety: Sunstone (red-orange gemstone)

Hierarchy of Mineral Classification: Mineral Classes Based on the anion or anionic buildings in the gem structure Types of holding and structures are the same (or comparative) Physical properties can be fundamentally the same as inside classes

Mineral Subclasses Classified on premise of structure Example: silicates Nesosilicates : SiO 4 , free silica tetrahedra Sorosilicates : Si 2 O 7 , twofold silica tetrahedra Cyclosilicates : SiO 3 , ring of silica tetrahedra Inosilicates : Si 4 O 11 , chains of silica tetrahedra Phyllosilicates : Si 2 O 5 , sheets of silica tetrahedra Tektosilicates : Si0 2 , systems of silica tetrahedra Hierarchy of Mineral Classification

Hierarchy of Mineral Classification Mineral Groups ; mineral species with close substance and auxiliary relationship e.g. (regularly because of nuclear substitution/strong arrangement) Example: Amphibole, Feldspar, Mica, Pyroxene, Garnet, Olivine, Spinel

Hierarchy of Mineral Classification Mineral Species " actually happening homogeneous crystalline substance of inorganic birthplace, having trademark physical pr