Mineralogy midterm

triclinic

a ≠ b ≠ c

α ≠ β ≠ γ ≠ 90°

nothing is equal

orthorhombic

a ≠ b ≠ c;

α = β = γ = 90°

all sides unequal, all angles 90

trigonal

all sides equal

no equal angles

tetragonal

a = b ≠ c

α = β = γ = 90°

rectangle sides, square tops

isometric

everything equal

cube

hexagonal

a=b≠c α=β=90 γ=120

monoclinic

a≠b≠c

α=γ=90°

β≠90°

no sides equal, two right angles

mineral

naturally occuring inorganic crystalline solid with a chemical formula

how to find coordination number

number of anions around a central cation

covalent bonding

electrons are shared

ionic bonding

electrons are transferred

Polymorphism and its types

minerals with a different structure but the same composition

-reconstructve

-displasive

-order

-polytypism

plane lattice

a=b

Y= 90

square

plane lattice

a≠b

Υ=90

rectangle p

a≠b’ & a≠b

cos(y’)=a/2b & Y=90

rectangle p

a=b & Y=120

hexagonal

a≠b & Y≠90

oblique

reconstructive polymorphism

major reorganization of the crystal structure- chemical bonds are broken and new bonds are formed

displasive polymorphism

distortion or bending of bond angles-small amount of energy is used, and the reaction is immediate and reversible

order polymorphism

structure remains the same, but cation distribution changes

polytypism

polymorphs differing in stacking of identical sheets or layers

solid solution

mineral structure where specific sites are occupied in variable proportions by two or more different chemical elements because of changing local condition

simple substitution solid solution

substituting cations with same charges

coupled solid solution

substitution where the charge balance is maintained