EOSC 118: Lesson 7 - Minerals: Parent Gem Minerals

apfu?

"Atoms per formula unit" = Used to represent the component elements and the number of atoms in each element written in a subscript of a mineral ex) SiO2

What are polyhedra composed of?

- A central cation carrying a positive charge - A number of anions carrying negative charges

Learning goals

x

What is a crystalline material?

A solid in which the component atoms are arranged in a particular, repeating, 3D pattern

Solid solution?

A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase.

Rocks are ______________ of minerals

Aggregates

What is the difference between reporting the composition of a mineral on an atom basis, atomic weight basis, and oxide weight basis?

Atom basis: - The total number of atoms in the compound ex) SiO2 = 3 atoms Atomic weight basis: - Find the percentage an element makes up of a compound ex) Atomic weight for SiO2 = 60 amu, Si = 28 amu and O= 16 amu. Si = 46% as 28/60 =0.46 Oxide weight basis: - Find the percentage of the oxide within the compound

Appreciate the three common ways of reporting a mineral`s composition (e.g., atom basis, atomic weight basis, and oxide weight basis)

Atom basis: - The total number of atoms in the compound ex) SiO2 = 3 atoms Atomic weight basis: - Find the percentage an element makes up of a compound ex) Atomic weight for SiO2 = 60 amu, Si = 28 amu and O= 16 amu. Si = 46% as 28/60 =0.46 Oxide weight basis: - Find the percentage of the oxide within the compound ********* CHECK BC THIS IS A GUESS

Distinguish between major, minor, and trace elements

Major: The elements that are fundamental in a mineral's chemical formula ex) Iron in Fe2SiO4 Minor: Elements are present in smaller amounts and commonly replace major elements in a mineral. They are sometimes a part of a mineral's chemical formula Trace: Elements that are found only in very small amounts and can either be a replacement for one of the major elements in a crystal structure or can be occupying "holes" in a crystal structure that are big enough for them to hide in. Rarely seen in a chemicals written formula

Describe the concept of charge neutrality in relation to minerals.

Minerals must maintain a neutral charge so they use opposite charges to cancel out any charges that the elements within the mineral may have

Are man-made (synthetic) crystals considered minerals?

Nope

Trace elements are always reported in what?

Parts per million (ppm) on an element weight basis

Weight percent?

The unit that mineralogists and geoscientists report the amount of a cation in

Recognize the "ball and stick" and "polyhedral" methods for constructing atomic models of crystal structures

These structures can connect to form intricate crystal lattices

What type of elements are chromophores usually found in? (major minor or trace)

Trace

Extract information from a mineral formula, such as the component elements and number of atoms of each element

easy as f SiO2 1 silicon 2 oxygen

Describe the ten main physical properties of minerals and how these are used to identify minerals

1) Colour 2) Luster - how it reflects light 3) Streak - colour of the powder 4) Cleavage - cracks within the crystal 5) Fracture - breakage not in straight lines 6) Tenacity - durability 7) Hardness - how difficult it is to scratch it 8) Refractive index - dispersion 9) Specific gravity - density 10) Fluorescence -UV light

Physical properties that are used to identify a mineral? (10)

1) Colour 2) Luster - how it reflects light 3) Streak - colour of the powder 4) Cleavage - cracks within the crystal 5) Fracture - breakage not in straight lines 6) Tenacity - durability 7) Hardness - how difficult it is to scratch it 8) Refractive index - dispersion 9) Specific gravity - density 10) Fluorescence -UV light

What are the six systems crystals can be classified into?

1) Cubic 2) Tetragonal 3) Hexagonal and trigonal 4) Monoclinic 5) orthorhombic 6) Triclinic

Be familiar with the six crystal systems and the concept of crystal habits

1) Cubic 2) Tetragonal 3) Hexagonal and trigonal 4) Monoclinic 5) orthorhombic 6) Triclinic Crystal Habits: a complete description of the external shape of a crystal, this includes all of its visible characteristics including it's face and its form

What are the types of crystal forms?

1) Cubic 2) dodecahedral 3) rhombohedral 4) If crystals from one system appear to have crystallized into a crystal of another system, it is referred to as a "pseudo"

What are the three types of crystal faces?

1) Prism 2) Pyramid 3) Pinacoid

State the two main properties that must be similar between elements in order for substitution to occur in a mineral

1) Similar charge 2) similar ionic radius

Silicon and oxygen make up about ______ of the earth's crust by weight?

3/4

Secondary mineral?

A mineral that has been produced throughout the alteration of a primary mineral after its formation

Primary mineral?

A mineral that has crystallized directly through some igneous, sedimentary or metamorphic process

Minor elements?

Elements are present in smaller amounts and commonly replace major elements in a mineral. They are sometimes a part of a mineral's chemical formula

Trace elements?

Elements that are found only in very small amounts and can either be a replacement for one of the major elements in a crystal structure or can be occupying "holes" in a crystal structure that are big enough for them to hide in. Rarely seen in a chemicals written formula

Chromophores?

Elements that cause colours in minerals?

Aggregates?

Groups of intimately associated crystals, growing in a group or a cluster

What type of processes form minerals?

Inorganic provesses

Appreciate that element substitutions occurs in minerals and describe the difference between simple and coupled substitution

Simple substitution: When one element substitutes itself in a chemical formula for just one other element Coupled substitution: When more than two elements are substituted in a chemical formula

Major elements?

The elements that are fundamental in a mineral's chemical formula ex) Iron in Fe2SiO4

Minerals are composed of how many chemical elements?

Two or more

Major elements are always reported in what?

Weight percent of the oxide

Minor elements are usually reported in what?

Weight percent of the oxide

Coupled substitution?

When more than two elements are substituted in a chemical formula

Simple substitution?

When one element substitutes itself in a chemical formula for just one other element

The Goldilocks principle?

When similar elements of the same size and charge can be interchangable

What does it mean to have an x-fold coordination? What does the X refer to?

When the cations and the anions of a polyhedron are interacting with each other, forming a structure The x refers to the number of atoms involved

Define crystal habits

a complete description of the external shape of a crystal, this includes all of its visible characteristics including it's face and its form

What is a mineral?

a naturally occurring homogeneous solid with a definite (but generally not fixed) chemical composition and a highly ordered atomic arrangement

Define polyhedra, or platonic solids

a solid figure with many plane faces that makes up the internal structure of the crystal lattice

A compound MUST be ______________

charge neutral