Minerals

Minerals

All the rocks and minerals in the Earth’s lithosphere are made of elements, but not all rocks are minerals.

To be classified as a mineral it must be:1. A solid 2. Naturally occurring3. Inorganic4. Have a crystal structure5. Has a definite chemical composition.

What are Minerals

There about 4000 known minerals, however of all the elements in the Earth’s crust, only a mere eight make-up 98.5% of the crust total mass. Of those eight elements, more 90% of the minerals are compounds containing only two.

1. Oxygen – 46.6% 5. Calcium – 3.6%2. Silicon – 27.7% 6. Sodium – 2.8%3. Aluminum – 8.1% 7. Potassium – 2.6%4. Iron – 5% 8. Magnesium – 2.1%

Minerals

The formation of minerals is a process known as crystallization.There are three main ways minerals crystallize:

1. Magma Process2. The Pressure Process3. Crystallization from solution

How do minerals Form?

Convection currents deep in the Earth’s mantle cause magma to rise and begin to cool. As the magma cools, atoms, molecules, and ions arrange themselves into regular, repeating patterns and bond forming various crystals.

Magma Process

1. Pressure chemically breaks down the rock

2. Heat and pressure change the rock’s properties without melting the rock

3. The atoms, ions, and molecules recombine to form new minerals

Pressure Process

When water cools or evaporates, the particles of dissolved minerals come together again and crystallize.

Crystallization From Water

Every mineral has a unique set of physical properties that are used to identify it. These properties include:

1. Color2. Luster3. Hardness4. Streak5. Cleavage 6. Fracture7. Density8. Specific Gravity

Mineral Identification

Color is the easiest of all properties to observe however, it is the least reliable.

Color

Luster describes the way a mineral surface reflects light. Lusters include:

1. Metallic2. Nonmetallic3. Greasy4. Dull5. Earthy6. Glassy7. Pearly

Luster

Metallic

Nonmetallic

Dull

Greasy

Earthy

Glassy

Pearly

Hardness is a mineral’s resistance to being scratched.Mineralogist Friedrich Mohs devised a numeric scale to determine the hardness of a mineral.

Hardness

The streak of a mineral is the color of its powder. Streak is obtained by rubbing the mineral on a streak plate.

Streak

Cleavage is a mineral’s tendency to split along smooth, flat surfaces.

Cleavage

Fracture occurs when a mineral breaks along rough or irregular surfaces.

Fracture

Special type of fracture that occurs in glassy type minerals.

Conchoidal Fracture

Many minerals have similar densities however, very high or low densities can be used to identify certain minerals.

Examples: Pumice: .64 g/cm3

Platinum: 21.5 g/cm3

Formula:

Density

A mineral’s specific gravity is the ratio of its dry mass to the mass of an equal volume of pure water. In general, the specific gravity of a mineral tells you how many times denser the mineral is than pure water.

Formula:

Specific Gravity = ______Dry Mass______ (Dry Mass) – (Wet Mass)

Specific Gravity

Some minerals have unusual characteristics that can be used to identify specific minerals.

Special Mineral Properties

Double Refraction occurs when a single light wave is split into two.Example: Iceland spar

Double Refraction

When certain minerals are exposed to ultraviolet light they will glow.

Fluorescent

Minerals such as calcite and halite have a salty taste.

Taste

Minerals such as lodestone and magnetite are naturally magnetic.

Magnetic

Some minerals such as carnotite and uraninite give off radiation that can be detected using a Geiger Counter.

Radioactivity

Minerals are classified according to similarities in composition. Minerals are classified into four main groups:

1. Silicates2. Carbonates3. Oxides4. Sulfides

Mineral Groups

Silicates are any minerals that contain silicon and oxygen. The basic building block of a silicate is the silica tetrahedron.

Silicates

Properties QuartzSiO2

Color Colorless, rose, amethyst,

smokyLuster GlassyHardness 7Streak WhiteBreak ConchoidalDensity 1.2 g/cm3

Specific Gravity 2.65Crystal Structure

Silica Tetrahedron

Special Properties

-

Major Silicates

The feldspar family makes up approximately 60% of Earth’s crustThe molecular difference between quartz and feldspar is that the silicone atom is replaced by either an aluminum,potassium, sodium, or calcium atom. Feldspar is classified into two main groups:

1. Orthoclase Feldspar: Potassium atom2. Plagioclase Feldspar: Sodium-calcium

atoms

Major Silicates cont.

Properties Orthoclase Feldspar Plagioclase Feldspar

Color Salmon with parallel white fibers

White to gray

Streak White White

Hardness 6 6

Luster Pearly Pearly

Crystalline Structure

Silica Tetrahedron Silica Tetrahedron

Break Cleavage (two directions)

Cleavage (two directions)

Density 2.55-2.75 2.55-2.75

Specific Gravity

2.5 – 2.6 2.5 – 2.6

Orthoclase Feldspar Plagioclase Feldspar

SilicatePyroxene Family: Ferromagnesian

Properties Augite(Ca,Na)(Mg,Fe,Al)

(Al,Si)2O6

Color Brownish greenLuster GlassyHardness 5 – 6.5Streak Greenish grayBreak CleavageDensity 1.2 g/cm3

Specific Gravity 2.65Crystal Structure

Silica Tetrahedron

Special Properties

-

Mineral in the mica family are soft silicates:Muscovite and Biotite are minerals that form flat crystals that cleave in only one direction to form thin sheets.

Silicate

A carbonate is a mineral made of negatively charged carbonate ions bonded to a positive metal ion. Each carbonate is composed of 1 carbon atom and 3 covalently bonded oxygen atoms.

Carbonates

Properties CalciteCaO3

Color Colorless/WhiteLuster GlassyHardness 3 – 3.5Streak WhiteBreak CleavageDensity 2.7 g/cm3

Specific Gravity 2.7Crystal Structure

Rhombohedra

Special Properties

Fluorescent

Acid Test Bubbles

Carbonate

Properties DolomiteCaMg(CO3)

Color WhiteLuster GlassyHardness 3.5 - 4Streak WhiteBreak CleavageDensity 2.48g/cm3

Specific Gravity 2.8Crystal Structure

Rhombohedra

Special Properties

-

Carbonate

Oxides are any mineral containing significant amounts of iron and oxygen.

Sulfides are any mineral containing significant amounts of iron and sulfur.

Oxides and sulfides are used in manufacturing to make steel, medicines, cosmetics, plastics, and paints.Any mineral that can be sold for a profit is known as anore.

Oxides and Sulfides

Properties HematiteFe2O3

Magnetite Fe3O4

PyriteFeS2

Color Black, Red Black, Brown, Gray

Pale to Bright Yellow

Luster Metallic, Earthy Metallic MetallicHardness 5 - 6 5.5 – 6.5 6 – 6.5Streak Red Black Greenish BlackBreak Fracture Fracture ConchoidalDensity 5.255 g/cm3 5.175 g/cm3 4.9 g/cm3

Specific Gravity 5.3 5 5Crystal Structure

Hexagonal Octahedral Cubic

Special Properties

- Magnetic -

Common Oxides and Sulfides

Hematite Magnetite Pyrite