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Chapter 5: Atoms, Elements, and Minerals
What are minerals?
•Compositionally and physically distinctive substances.
•Develops in a particular way under natural conditions such as heat,
pressure, oxygen, available atoms, and acid content determine how
minerals are formed.
•4500 kinds of minerals in the world- only a couple hundred that are
common and a couple dozen that for the majority of all rocks.
•Distinguished by properties such as, colour, luster, hardness, chemical
composition and the transmission of light under a microscope.
•Crystals are “perfectly formed’ minerals. Consist of faces, edges and
•A geode–pocket of volcanic rocks–forms crystals with faces that reflect
•There are 230 different kinds of symmetrical arrangements in nature.
•Minerals are said to be crystalline because of this universal property.
•A crystalline: substance is one in which the atoms are arranged in a
three-dimensional, regularly repeating, orderly pattern.
•Minerals can be defined as a family
What are atoms and elements?
•Atoms:” smallest electrically neutral assemblies of energy and matter.
•They contain electrons that carry a negative charge and move in the
direction that allow them to neutralize their charge by crowding
around positively charged protons.
•The nucleus contains neutrons which are neutrally charged particles.
•92 naturally occurring atoms, each called an element.
•An element, is defined by the number of protons in its nucleus.
•Electrons in an atom are continuously on the move, spending most of
its time as part of an energy level.
•The stable configuration is to have a completed energy level.
•The first is complete with 2, second and third level are complete with 8
•The bonding of atoms to for minerals takes place when an atom has a
deficit or surplus of electrons in their outer most energy level.
•An electrically charged atom is called an ion.
Ions and Crystalline Structures
•Positively charged ions are called cations (excess positive charge)
•A negatively charged ion is called an anion (excess negative charge)
•There are several factors that cause ions to bond together to form a
oNeed for different ions of like-charge to be as widely separated
as possible. (Ions only come close to form a stable mineral
structure because they are “glued” into place by bonding with
ions of the opposite charge)
oNeed to neutralize electrical charges
•Electrons have different ionic radius from it’s nuclei. Ionic radii plays
an important role in the arrangement of atoms in a crystalline structe.
•When ions come together they pack as efficiently as possible.
•Many anions may crowd around a large cation, while few large anions
cluster about a small cation.
•An example of the above are the elements in the earth’s crust– oxygen
The Silicon-Oxygen Tetrahedron
•Silicon and oxygen form the atomic framework for most common
minerals on earth.
•The basic structural unit is 4 oxygen atoms packed around a single
smaller silicon atom.
•The four-sided pyramidal geometric chap called a tetrahedron
represents this structure
•Each corner of the tetrahedron represents the centre of an oxygen
•The basic building block of a crystal is called a silicon-oxygen
•The atoms of a tetrahedron are strongly bonded together.
•The negative charges exceed the positive charges.
•The silicon-oxygen tetrahedro can either bond with positively charged
ions, or with other silicon-oxygen tetrahedrons.
•In order for it to be stable, it must ever 1. Be balanced by enough
positively charge ions or 2. Share oxygen atoms with adjacent
•Structes of silicate minerals range from an isolated silicate structre, to
•Isolated silicate structure: silicate minerasl that are structured so that
none of the oxygen atoms is shared by tetrahedrons. Bounded together
by positively charged ions. E.g. olivine.
•Chain silicate structure: two of a tetrahedron’s oxygen atoms are
shared with adjacent tetrahedrons to form a chain. Has a net excess of
negative charges. May have single or double-chain structures. Single