Copyright: Foundations of Earth Science, 7th ed

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Minerals

Building Blocks of Rocks

mineralogy: study of minerals

Minerals: Naturally occurring, inorganic, solid with crystalline structure & defined chemical & physical properties that allow it for some variation

Naturally occurring: Form by natural geologic processes, so Synthetic materials are not considered minerals

Inorganic: Crystalline solids from organic sources are not minerals
Some organisms secrete inorganic compounds like calcium carbonate, these material considered a mineral if they become part of the rock record

Solid exception is mercury –> liquid

Crystalline structure Atoms arranged in an organized, & repetitive manner, Organization is reflected in the crystal shape

Chemical composition that allows for some variation: Most minerals are compounds so can be expressed as a chemical formula such as quartz SiO₂
– Composition vary due to substitute for elements & substituting of elements have the same size will not change the crystalline structure of the mineral

Important in human history
1. Flint & chert for weapons & tools
2. Gold, silver, & copper mined by Egyptians
3. Bronze developed by 2200 BC
4. Mining became common by Middle Ages

rocks

naturally occurring solid aggregate mass of mineral, or mineral-like matter

Most aggregates of several different minerals

Individual properties of the minerals are retained

Some rocks are composed of a single mineral, Such as limestone → calcite

Some rocks  made of non-mineral, Such as obsidian & pumice (glass), & coal (organic)

Atoms

Building Blocks of Minerals

All matter, including minerals, is composed of atoms, & All atoms (excluding H & He) formed inside massive stars by fusion

Atom: the smallest particle that cannot be chemically split

Protons, Neutrons, & Electrons

Protons & neutrons have almost identical masses, & Electrons are much smaller (1/2000) than protons & neutrons

Protons +ve
Found in the nucleus
atomic number: number of P⁺ in the nucleus, & Determines chemical nature of atom
element: atom with the same atomic number

Electrons – ve
Surround the nucleus like a cloud
Valence electrons interact to form bonds
Move around the nucleus in a cloud with different regions called principle shells
Each principle shell has an energy level & a specific number of electrons
The outer shell contains valence electrons
Interact with valence electrons of other atoms to form chemical bonds

Neutrons no charge
Found in the nucleus

Most matter is neutral, because the charges of P⁺ & e- cancel each other out

Atoms Bond

Elements (excluding noble gasses) form bonds under the T & P conditions that occur on Earth
Bonds lower the total energy of the atoms & make them more stable

A chemical bond

transfer or sharing of electrons that results in a full valence shell

Ionic bonds: electrons are transferred
Covalent bonds: electrons are shared
Metallic bonds: electrons move around

Ionic Bonds

Electrons Transferred

When one atom loses or gains valence electron, ions are formed
1. Electrons are lost: becomes +ve ion
2. Electrons are gained: becomes – ve ion

Ionic bond form when ions with opposite charges attracted, & Creates ionic compound

Ionic compounds have very different properties than the bonded elements that make them up

Metallic Bonds

Electrons Free to Move

form when valence electrons are free to move from one atom to another

All atoms share available valence electrons
Movement of e- between atoms results in:
1. High electrical conductivity
2. Malleability
3. Other unique properties of metals

Physical Properties

Minerals have a definite crystalline structure & chemical composition that Gives them unique physical & chemical properties & These properties can be used in identification

Include
Luster
Ability to transmit light
Color
Streak
Crystal Shape or Habit
Strength (Tenacity, Hardness, Cleavage, Fracture)
Density & Specific Gravity
other distinctive properties (Taste, Feel, Smell, Magnetism, Optical properties, & Effervescence)

Luster

quality of light reflected from the surface of a mineral

Types of Luster
metallic: Minerals that look like shiny metal
submetallic: appears slightly dull
Nonmetallic: Vitreous or glassy, dull, earthy, pearly, silky, & greasy

Ability to transmit light

opaque: do not transmit light are
translucent: transmit light, but not image
transparent: transmit both light & images

Color

may be one of the most obvious properties of a mineral, but it is only a diagnostic property for a few minerals

Slight variations in the chemical composition can change the color dramatically

Streak

is the color of a mineral in powdered form
Obtained by rubbing the sample on an unglazed porcelain tile (streak plate)
Streak, unlike color, is generally consistent
Metallic minerals have a dense, & dark streak
Nonmetallic have a light streak
Not all minerals produce a streak

Crystal shape or habit

is the characteristic shape of individual mineral crystals
Most minerals grow in one common shape, but some have 2 or more shapes

strength

determined by the strength of chemical bonds & determines how minerals break or deform under stress

Include
Tenacity, Hardness, Cleavage, Fracture

Tenacity

resistance to breaking or deforming

Minerals with ionic bonds tend to be brittle, shatter under stress

Minerals with metallic bonds are malleable, deformed into shapes & thin sheets

Sectile minerals cut into thin shavings

Elastic minerals return to its original shape after being bent

Hardness

resistance to abrasion or scratching
measured on a scale of 1 to 10 (Moh’s Scale)
Can be determined by rubbing the mineral against a material of known hardness

Cleavage

tendency of a mineral to break along planes of weak bonding
This produces smooth, & flat surfaces
Not all minerals have cleavage
Cleavage easily confused with crystal shape
cleavage is visible when a mineral is broken

Fracture

property resulting from chemical bonds that are approximately equal in strength
Irregular: uneven broken surface
Conchoidal: smooth, curved broken surface
Some minerals exhibit splintery or fibrous broken surfaces

Density & Specific Gravity

Specific gravity describes the density
Specific gravity G: Ratio of a mineral’s weight to an equal volume of water
Most minerals have G between 2 & 3
Many of the metallic minerals have a much higher G (20 for gold)
G estimated by hefting mineral in your hand

other distinctive properties

Taste halite is salty
Feel talc is soapy, & graphite is greasy
Smell sulfur smells like rotten eggs
Magnetism some can be picked up by a magnet & some can pick up iron objects
Optical properties calcite refracts light
Effervescence carbonate minerals fizz when exposed to dilute acid HCl

Mineral Groups

There are > 4000 named minerals, but only a few are abundant in Earth’s crust known as rock-forming minerals

Economic minerals are less common than rock-forming minerals, but are used in the manufacture of products

silicate groups: Silica & oxygen combined to form the basic building block for the silicates
The most common minerals
More than 800 silicate minerals
Make up 90% of the Earth’s crust

The remaining mineral groups referred to as the nonsilicates
Far less abundant in Earth’s crust
Some are very important economic minerals

Silicate Minerals

Feldspars are the most common silicates, > 50% of Earth’s crust

Quartz is second-most abundant mineral in continental crust

Only common mineral composed completely of Si & O

Silicate minerals tend to cleave between the strong silicon-oxygen structures

Most silicate minerals crystallize from molten rock as it cools

Environment & chemical composition determines which minerals are produced

Some silicate minerals form at Earth’s surface as other silicates are weathered

Some silicate minerals form at extreme pressures during mountain building

Summary

Minerals divided into rock forming menirals that form solid earth & Valuable (economic value), Both may be Silicates or Non-silicates

Silicates (the most common) are based on the
silicon-oxygen tetrahedron, Subdivided into light & dark groups

Nonsilicates include -ve ion, common in sedimentary rocks, & Many ot them are economically important

The End