Lecture 5: Mineral Properties

Atom

Composed of an electron made up of negatively charged electrons and a nucleus

• Nucleus has about the same number of positive protons and neutral electrons
• Outer shell has about the same number of negative electrons

Element

A grouping of the same atoms that all have the same number of protons

• Example: carbon, oxygen, uranium
• Isotope - elements with the same atomic number but different number of neutrons

What is a Mineral?

Mineral - A material composed of a single or multiple elements held together by chemical bonds

• Covalent ionic bonds are strong
• Metallic bonds are weaker
• Van der Waals bonds are the weakest

Fundamental Properties of Minerals

• Naturally occurring - produced in nature

Solid - can maintain its shape

Inorganic - sugar and protein are not minerals

• Crystalline structure (orderly internal arrangement) - structure is fixed
• Definable chemical composition - possible to write a chemical formula for it

Is Ice a Mineral?

• Naturally occurring: Yes
• Solid: Yes when it is cold out
• Crystalline structure (orderly internal arrangement): Yes
• Definable chemical composition: Yes (H2O)
• Inorganic: Yes

Mineral Properties

• Color
• Streak - Rubbing the material against a porcelain plate
• Luster - the way a mineral surface scatters light, can be metallic or non-metallic
• Hardness - ability to resist scratching, Mohs scale
• Specific Gravity
• Crystal Habit - shape/ structure of a mineral
• Cleavage - how a mineral breaks
• Other - reacts with acid, magnetic, salty, etc

Mohs Hardness Scale

• Measure of the relative ability of a mineral to resist scratching

Cleavage vs. Crystal Habit

Crystal form - shape of a crystal. Crystal face is a single surface

Cleavage - tendency of the crystal to split along definite structural planes

• Forms in directions where bonds holding atoms together in the crystal are the weakest
• Cleavage planes can be repeated

Ionic Bond

• Atoms EXCHANGE but DO NOT SHARE electrons
• Atoms are then attracted to each other because of their charge
• Example: Halite; mystery mineral #1
• 3-sided crystal form right angles, 3 directions of weakness, can be easily dissolved

Covalent Bond

• Atoms SHARE electrons to make themselves more stable
• Example - Diamond
• Carbon atoms are arranged in a tetrahedral, all bonds are strong (covalent)
• Example - Graphite
• Carbon atoms arranged in hexagonal sheets, sheets are connected by weak bonds (van der Waals)