Chapter 3- Interlude A

Atoms

• Building blocks of minerals

• Elements form chemical bonds with other elements to form chemical compounds

• Neutron and Protons (+) in the nucleus

• Electrons (-)

Types of Atomic Bonds

• Ionic Bond

  • Between positively and negatively charged atoms (ions)

  • Coulomb’s Law: opposite charges attract

• Covalent Bond

  • Between atoms sharing valence electrons

• Metallic Bond

  • Each atom contributes to a pool of valence electrons

  • Gives metals their electrical conductivity

Ionic Bonding of Sodium Chloride

A- the transfer of an electron from a sodium (Na) atom to a chlorine (Cl) atom leads to the formation of a Na ion and a Cl ion

B- The arrangement of Na and Cl in the Solid ionic compound sodium chloride (NaCl) AKA halite, salt

Lattice

3D array of regular spaced points

Crystalline material

Atoms situated in a repeating 3D array

Amorphous materials

Material with no such order

Unit cell

Basic building block unit (such as a flooring tile) that repeats in space to create the crystal structure.

Mineral

1- Naturally Occuring

2- Inorganic

3- Solid

4- Ordered crystal structure

5- Definite chemical composition

Rock

A solid mass of mineral or mineral-like matter that occurs naturally

Crystalline Structures

• Crystalline: most solid materials

• Glasses: solids lacking internal atomic order (aka amorphous)

Crystal

• A single, continuous piece of crystalline solid typiclly bounded by flat crystal faces.

• Ordered atomic arrangement inside minerals imparts symmetry to crystals

• Equivalent faces found on two samples of the same mineral always bear the same angular relationship.

Types of Mineral Crystals

Polymorphs

Minerals that share the same chemical composition but have different crystal structures.

Synthetic Minerals

“Man-made” lab-grown equivalents to minerals

Mineral Formation

• Crystallization of a melt

• Precipitation from aqueous solution

• Precipitation by organisms (biomineralization)

Crystal Growth

• Early crystals act as a seed for further growth of the mineral

• As crystals grow, they often encounter other growing crystals

• Mineral growth is often restricted by space, which prevents development of good crystal faces.

Mineral Identification

Based on:

• Color: can be diagnostic of some minerals, but poor indicator for others.

• Luster

• Streak

• Hardness

• Specific gravity

• Crystal habit

• Cleavage

• Reaction to acid

• Fracture tendency

Luster

The way a mineral surface scatters light, can tell us if it is metallic or nonmetallic.

Streak

Color of a mineral in powdered form, rubbed against a streak plate. Mostly useful to identify metallic minerals.

Hardness

Measure of resistence to abrasion or scratching. Mohs Scale of Relative Hardness. Diamond is the hardest (10), Talc the softest (1)

Crystal habit

Common of characteristic shape of individual crystals or aggregates of crystals.

Cleavage

The tendency of mineral to break along plans of weak bonding.

Described as the number of cleavage directions/planes and the angles at which they meet. e.g. two planes at 90 degrees

Fracture

When a mineral has no weak bonds, it will fractire )it has no cleavage planes)

Density- Specific Gravity

Ratio of minerals weight to wieight of equal volume of water

• Most common minerals: 2-3

• Metallic minerals higher, more dense.

Other distinctive properties

• Reaction with acid (effervescence) e.g. Calcite reacts with acid

• Magnetism, e.g. Magnetite

• Taste, e.g. Halite (salt)

• Smell, e.g. Sulfur

• Feel, e.g. Talc (feels greasy)

• Double refraction, e.g. (calcite or quartz)

What elements make up the majority of earth’s rock-forming minerals?

• Silicon (Si)

• Oxygen (O)

• Aluminum (Al)

• Iron (Fe)

• Calcium (Ca)

• Potassium (K)

• Magnesium (Mg)

Minerals that make up most of the Earth

Silicates

• Feldspars

• Quartz

• Amphiboles

• Micaas

• Olivine

• Garnet

• Pyroxene

• Calcite (not a silicate)

Common Mineral Groups

Minerals that share the same basic “building block”

• Silicates (SiO4)

• Sulfides (S2)

• Oxides (O2)

• Halides (Cl1,F1,Br1)

• Carbonates (CO3)

• Sulfates (SO4)

• Native elements

Silicates

• Most abundant class of minerals in Earth’s crust

• Oxygen and Silican in combination

• Classified into:

  • Mafic (less % silica)

  • Felsic (more % silica)

• Quartz

• Olivine

Isolated Tetrahedra Silicates

Do not share any oxygens, they are bonded together by cations.

Garnet and Olivine

Single-Chain Silicates

Form chains by sharing two oxygen atoms.

Pyroxene

Double-chain silicates

Share two or three oxygen atoms

Amphibole

Sheet Silicates

• All tetrahedra share two or three oxygens to form 2D sheets

• Have cleavage in one direction

• Muscovite Mica and Biotite Mica

Framework Silicates

• Share all four oxygens

• Form 3D structure

• Feldspars

What holds a rock together?

• Clastic rocks: Natural cement bonds together the grans of some rocks (sndstone)

• Crystalline rocks: others are held together with interlocking minerals crystals (granite)

Bedrock

• Rock that remains attached to the Earth’s crust

• An exposure of berock is called an outcrop

• Bedrock exposures can be either natural or man-made

Rock cycle

Other Rock Cycle diagram