Patterns in Nature Minerals Lecture 8 Minerals The building blocks of rocks and hence of Earth More than 4 000 are known New minerals are discovered annually Developed societies depend on mineral resources Economically important drives world economies Historically important dictated human history What is a Mineral Naturally occurring Solid Crystalline orderly internal structure atoms arranged in a definite pattern Definite Chemical composition Definition of Mineral A mineral is a naturally occurring solid with a highly ordered atomic arrangement and definite but not fixed chemical composition It is usually formed by inorganic processes Rocks Rocks are Earth material made from minerals Most rocks have more than one kind of mineral Some are monomineralic Chemical Concepts Element substance that cannot be separate into other elements Atom smallest particle of an element that retains chemical properties Nucleus core of atom containing protons and neutrons Subatomic particles Neutrons electrically neutral subatomic particle Protons positively charged subatomic particle Electrons negatively charged subatomic particle Atomic number number of protons in nucleus Number of protons unique to each element Atomic weight number of protons plus number of neutrons Isotopes are atoms of the same element with differing numbers of neutrons Ions Bonding When an element has the same number of protons and electrons it is neutral w no charge Unequal number of electron and protons a net electrical charge an ion Molecule or compound two or more atoms bonded together Bond interaction between two or more atoms that holds them together The type and strength of bonding govern mineral properties 5 recognized types of bonds Covalent sharing of electrons Metallic sharing of free electrons among a lattice of metal atoms atoms in Ionic bond between a metal and a non metal sea of electrons high conductively Van der Waals a secondary interatomic bond between adjacent molecular Hydrogen the attractive interaction of a hydrogen atom with an electronegative atom that comes from another molecule dipoles Polymorphs Same composition but different crystal structure Diamond and graphite are carbon polymorphs Mineral Physical Properties Characteristics determined by your 5 senses Used to ID minerals Properties depend upon Chemical composition Crystal structure Some are diagnostic Minerals have a unique set of physical properties Color Color is diagnostic fro some minerals Some minerals may exhibit a broad color range Color varieties often reflect trace impurities Streak Hardness Luster Color of a mineral crushed on unglazed porcelain Streak is often diagnostic property Scratching resistance of a mineral Hardness compared to the Mohs Hardness Scale Is it dull or reflected Specific Gravity Related to density mass per volume Mineral weight over weight of equal water volume Specific gravity is heft how heavy it feels Pyrite feels heavier then feldspar Crystal Habit Crystal Form Cleavage cleavage Crystal habit shape of a single well formed crystal Crystal habit is the ideal shape of crystal faces Ideal growth requires ideal conditions many terms are used to describe habit Minerals vary in crystal face development Euhedral crystal a crystal displaying well formed faces Anhedral crystal a crystal without well formed faces Anhedral crystals are more common than Euhedral Cleavage a mineral that regularly breaks along a predetermined plane has Cleavage planes can be repeated crystal faces are a single surface Conchoidal Fracture curving surfaces formed in some minerals that break without cleavage
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