Minerals

Review of Elements  An element is a substance that can not be broken down into other substances.  113 known elements (92 occur naturally)  Periodic table of the elements  Examples – Oxygen, hydrogen, gold…

Review of an Atom  An atom is the smallest possible particle of an element that still has all the properties.

Review: Parts of an Atom  Electrons - (negative charge) Orbit around the nucleus in energy levels or shells  Protons - (positive charge) Located in nucleus  Neutrons – (neutral charge) Located in nucleus

Atomic Number  Atomic number – represents the number of protons in an atom.  Neutral atoms have the same number of protons (+ charge) and electrons (- charge)  The atomic number is used to organize elements in the periodic table

Examples of Atomic #, Atomic Mass Number

Atomic Mass and Isotopes  Atomic mass – Total number of protons and neutrons (in nucleus)  Number of neutrons in an atom can change without affecting the atom. Elements containing different numbers of neutrons are called isotopes ex) Carbon 12 vs. Carbon 14

Forming Minerals  Some minerals can form from one element only. Example. Gold (Au)  Most minerals form when they one or more elements combine together. Example quartz (SiO 2 )

How do elements bond together?  Elements bond together by sharing their electrons known as covalent bonding  Electrons are given or taken away from one element to another ionic bonding

The Chemistry behind Table Salt  Chemical formula is NaCl  Composed of Sodium (Na) and Chloride (Cl)  Alone, sodium is soft, shiny, potentially explosive  Alone, chloride can be a toxic gas  Together they form harmless and essential table salt

Most common minerals  Of the 92 naturally occurring elements, only 8 make up 98% of the Earth’s crust  Two very important elements oxygen and silicon. They combine covalently to form a 4-sided pyramid (known as a: tetrahedron)  Minerals containing silicon-oxygen tetrahedron are called silicates (make up 1/3 of the minerals on Earth)

Definition of a mineral  A naturally occurring solid that is crystalline (repeating arrangement of atoms) and has a specific chemical composition (chemical formula).

Quartz crystals with Hematite "rosettes”

Orange Zircon Tourmaline “watermelon”

More about minerals…  Minerals are the building blocks of rocks.  4000 minerals have been identified  A mineral must: Occur naturally Have a chemical composition (formula) Contain crystals (chrystalline)

Mineraloids:  A mineral that does not have all three defining characteristics.  Example: Opal, Chrysocolla

How do geologists identify minerals?  To identify an unknown mineral, you should:  first determine its physical properties,  then match the properties with the appropriate mineral, using a mineral identification key.

Physical Properties of Minerals  To identify a mineral, geologists will study various physical properties: 1.Colour 2.Streak 3.Lustre 4.Hardness 5.External crystal form 6.Cleavage 7.Fracture 8.Specific gravity 9.Other: Chemical tests

1) Color  not always reliable because color can be changed by the presence of impurities within the mineral, by the type of light used (natural, artificial), by weathering of the mineral’s surface.  Azurite is always blue, malachite is always green.

2) Streak  Color that is displayed when the mineral is rubbed across a streak plate (more reliable than just external color).  Streak color will not always be the same as the color of the mineral.  Galena streaks gray; Hematite streaks red.

3) Luster  how the mineral’s surface reflects light (shiny, glassy, silky, pearly, etc.)  Galena has a metallic luster

4) Hardness  The “scratchability” or hardness of a mineral.  For a true hardness test, the hardner mineral or substance must be able to make a groove or scratch on a smooth, fresh surface of a softer mineral.  Example…

Example of hardness test: Quartz  Quartz can always scratch calcite

Mohs’ hardness Scale  10 minerals are designated as standards of hardness. Softest mineral = talc Hardness mineral = diamond 8mH9zw 8mH9zw

Mineral Hardness Hardness of Some Common Objects Talc1 Gypsum2 Human fingernail (2.5) Calcite3 Copper penny (3.5) Fluorite4 Apatite5 Glass (5-6) Pocketknife blade (5-6) Orthoclase (potassium feldspar)6 Steel file (6.5) Quartz7 Topaz8 Corundum9 Diamond10 Mohs Hardness Scale Incr easi ng hard nes s Increasing Hardness

Hardness Test…  Geologists rely on common objects to test for hardness. Fingernail usually has a hardness of about 2.5  If you can scratch a mineral with your fingernail it has a hardness of less then 2.5. A penny has a hardness between 3-4 A knife blad or a steel nail generally has a hardness of slightly greater than 5. Glass has a hardness of ~ 5.

How to conduct a hardness test on a mineral:  Website:  Video Clip

Mohs’ Scale Activity  Complete activity sheet

5) Crystal Form  The set of faces that have a definite geometric relationship to one another.

Examples ZIRCON GYPSUM RHODONITE QUARTZ

6) Cleavage  tendency to break consistently along distinct planes.  Example, halite always forms cubes

7) Fracture  When minerals don’t cleave, they fracture – break at random, forming jagged, irregular surfaces.

8) Specific Gravity  is a comparison of the weight of the mineral to the weight of an equal volume of water.  Example: GOLD has a specific gravity of 19.3, which means that it weighs 19.3 times as much as an equal volume of water.

Specific Gravity…  Specific gravity can be used to distinguish gold from pyrite (fools gold) which has a specific gravity of only ~4.

9) Other Tests: Smell and Taste  sulfur-containing minerals stink like rotten eggs  halite is salty tasting Sulfur Halite