THEME: To elucidate the principles governing the organization of matter into minerals.

KEY QUESTIONS:
Why is there a great diversity of mineral species?
Why are minerals indispensable to human health, welfare and standard of living?
How can the study of minerals reveal information about the physical and chemical conditions existing at the time they were formed?

OUTLINE:
Mineral: naturally occurring inorganic solid; possesses a crystalline structure and a chemical composition which is either fixed or which varies within limits.
Crystal: a solid bounded by smooth plane faces which are related to the solid's crystalline structure.
Mineraloid: naturally occurring solid or liquid which lacks a crystalline structure.
Rock: an aggregate of one or more minerals.
Central concept in Mineralogy: a mineral's crystalline structure and chemical composition control all of its properties.

HISTORICAL PERSPECTIVE:
Agricola (1546) - described mixing practices of the time
Steno (1669) - angles between corresponding faces on quartz faces are constant.
Huay (1743-1822) - offered an explanation for the development of crystal faces.

To understand minerals we must consider:
a) available chemical ingredients (elements)
b) the chemical nature of the available ingredients
c) the forces which "glue" the ingredients together
d) the relative sizes of chemical ingredients (ions)

There are over 3000 mineral species yet the Earth's crust is dominated by relatively few minerals.
The periodic table arranges elements according to their chemical behavior.
The forces which glue ions together are electrical in nature and can be described in terms of two ideal bond types (ionic & covalent).
Weak bonds produce soft minerals with low melting points; strong bonds produce hard minerals with high melting points, i.e. bond strength influences physical properties of minerals.
Coordination number = number of ions that surround and touch a given ion.
Radius ratio = radius cation/radius anion; allows us to predict the coordination number.
The coordination number for Si surrounded by oxygen is 4 - silicon-oxygen tetrahedron.
The silicon-oxygen tetrahedron has a net charge of -4 and is the basic building block of silicate minerals.
The great diversity of silicate minerals results from the number of shared corners (tetrahedron never share edges or faces) amongst the silicon-oxygen tetrahedra which is related to the temperature of formation.

Observed Linkages: Number of Shared Corners
-isolated tetrahedra (0 shared corners)
-paired tetrahedra (1 shared corners)
-rings (2 shared corners)
-single chains (2 shared corners)
-double chains (2-1/2 shared corners)
-sheets (3 shared corners)
-frameworks (4 shared corners)

As the temperature of formation decreases:
a) number of shared corners increases
b) the percentage of Si incorporated by the minerals increases
c) the density of the mineral decreases

Solid (= crystalline) solution: - solids may form true solutions (homogeneous mixtures) just as liquids and gases do provided that the following constraints are obeyed:
a) the ions which substitute for one another must have similar ionic radii (i.e., within 10-20%)
b) the resulting compound must be neutral

1. Although there are over 3000 known mineral species, the Earth's continental crust is dominated by a small number of minerals.

a. What is the most abundant silicate mineral group in the crust?
b. Why is this group so abundant?
c. Describe or illustrate the basic building block of this mineral group.
2. A fundamental building block of silicate minerals is the silicon-oxygen tetrahedron.

a. Briefly state why silicon and oxygen assume a tetrahedra arrangement.
b. What factor(s) govern the manner in which the tetrahedra are polymerized (linked up).
c. Select a common silicate mineral and illustrate the manner in which its tetrahedra are linked.
3. Define a mineral. Under what circumstances would ice be considered a mineral? Under what circumstances would it not be considered a mineral? How does a mineral differ from rock?
4. Briefly discuss ionic and covalent bonding in minerals. How do chemical bonds influence the physical properties of minerals?
5. Would changing an element's isotopic composition affect the physical properties of a mineral which incorporated that element? Briefly explain your answer.
6. What is ionic substitution and how is it related to solid or crystalline solution? Are there any limits to ionic substitution in minerals? How does ionic substitution influence the physical properties of minerals?

Abundance of Major Elements in Continental Crust
 

Element	Weight %	Atomic %	Ionic volume %
O2	47.2	61.7	93.8
Si	28.2	21.0	.9
Al	8.2	6.4	.5
Total Fe	5.1	1.9	.4
Ca	3.7	1.9	1.0
Na	2.9	2.6	1.3
K	2.6	1.4	1.8
Mg	2.1	1.8	.3
H tr	Trace	1.3	0

Estimated Mineralogic Constitution of Continental Crust
 

Mineral Groups	Volume %
Feldspars	58
Pyroxenes, amphiboles	13
Quartz	11
Mica, Chlorite, clay	10
Carbonates, oxides, sulfides, halides	3
Olivine	3
Epidote, Al-silicates, garnet, zeolites	2