What is a Mineral?

What Exactly is a Mineral? Compositionally and physically distinct substance Four criteria to be a true mineral…

Naturally Occurring Created through natural geologic processes Synthetic diamond: not a mineralRaw diamond: mineral

Inorganic That is, they do not consist of carbon-hydrogen molecules that may also form crystalline substances through biological processes Sugar: It looks like a mineral, but is it? Nope. Note the C-H bonds.

Solid Liquid waterSnowflake—frozen water Not a mineral Mineral…believe it or not

Definite Chemical Composition Minerals are complex assemblages of multiple elements Chemical Formula Types of atoms involved and relative proportions Ex. Quartz Chemical formula SiO 2 Ex #2: Elbaite Chemical formula Na(Li,Al) 3 Al 6 (BO 3 ) 3 Si 6 O 18 (OH) 4

Elements Pure chemical substance composed of one type of atom (i.e. specific # of protons…) 88 naturally occurring elements Most common (i.e. compose 98% of the earth’s crust—and therefore, minerals) – Oxygen, silicon, aluminum, iron, calcium, magnesium, potassium, and sodium

Atomic Structure Atom – Basic unit of an element – Very, very, very small (1/10,000,000,000 m) – Nucleus – Protons (+) – Neutrons (neutral) – Electrons (-) – “cloud” surrounding nucleus—exist in “shells” – Mostly empty space

Visualizing the size of an atom The nucleus is very small compared to the overall size of an atom Imagine 5 ½ football fields (minus end zones) placed end to end (100 yrds long x 160’ wide) Nucleus is like a grain of sand in the middle of them

It’s All About the Electrons, Baby… A stable atom is one in which the outermost shell of electrons is completely filled Atoms can fill their outer shells by bonding to other atoms – Ionic bonding – Covalent bonding

Bonding in a [Nut] Shell… Ionic Bonding – Cations (atoms that have lost an electron) are attracted to anions (atoms that have gained an extra electron) – Neutral compounds – Weaker but more common than covalent bonds

Bonding in a [Nut] Shell… Covalent bonding – Two or more atoms share their electrons, producing the effect of filled outer electron shells – Very strong bond

Crystalline Structure Arrangement of atoms are – Orderly – Regular – 3-D – Repeating pattern Halite Biotite Fluorite

Can You Spot the Mineral Wannabes? Pyrite FeS 2 oil Chalcanthite CuSO 4 -5H 2 O Silicon Carbide SiC

Growing a Mineral Unit cell—smallest unit structure of a mineral Brick Wall example

Growing a Mineral: Halite Halite unit cell Halite crystal What halite looks like to us

Identifying a Mineral All minerals have physical and chemical properties that can be easily recognized Direct result of structure and composition Crystal habit Cleavage Fracture Hardness Color Streak Luster

Cleavage Not the kind you’re thinking of… The tendency of a mineral to break along flat surfaces Governed by bond strength and crystal structure Stronger bonds = poor or no cleavage→

Oooo…shiny! Luster – The way a mineral reflects light A metallic mineral is said to have a metallic luster Those that do not have a metallic luster (non- metallic) are assigned names that are self- explanatory – Pearly, resinous, earthy, glassy, etc… Pyrite has a metallic luster Quartz has a glassy luster

School of Hard Knocks… Hardness – Resistance of a mineral to scratching Hardness can be determined by scratching mineral with an object of known hardness Scale—Mohs – Based on 10 minerals: 1 being talc and 10 being diamond