Minerals

How do we use Earth Materials?

• Earth Materials: minerals, rocks, and mineral resources (95% to 100% of objects you use)

What is a mineral?• Mineral: a naturally occurring, inorganic,

crystalline solid that has a definite chemical composition.

1. Naturally Occurring: a mineral must be formed by nature and not made by people.

What is a mineral?2. Inorganic: a mineral CANNOT form from

materials that were once part of a living thing.

What is a mineral?3. Crystalline solid: a mineral is always a solid, with

its own unique crystal structure.

What is a mineral?4. Definite Chemical Composition: a mineral always

contains certain elements in definite proportions.

Quartz Gold

Mineral or NOT?• Rock salt–AKA Halite–NaCl

• Beach sand–AKA tiny pieces of Quartz–SiO2

–Crystal shape is a pyramid

Mineral or NOT?

• Snow–Occurs naturally

Mineral or NOT?

• An ice cube

Mineral or NOT?

How are Minerals Related to Rocks?

• A rock is any naturally formed solid that is part of Earth or any other celestial object.–Organic or glassy rocks are NOT minerals.

How are Minerals Related to Rocks?

• There is only a small number of minerals commonly found in rocks.

Mineral Crystal Structure• A mineral’s atomic arrangement is responsible for

many of its chemical and physical properties.

Silicate Minerals• What two elements, by mass, make up the

greatest percentage of the Earth’s crust?

These two elements combine to form compounds called silicates.

The mineral Quartz is a type of silicate (SiO4)

They (Silica and Oxygen) combine in a specific structure called a: Silicon-oxygen tetrahedron.

Draw this structure below.

O

O

OO

Si

Mineral FormationMinerals can form in TWO ways:1. Crystallization of molten material2. Crystallization of materials dissolved in water.

Salt on a stone of the Dead Sea, Israel

Massive beams of selenite dwarf human explorers in Mexico's Cave of Crystals, deep below the Chihuahuan Desert. Formed over millennia, these crystals are among the largest yet discovered on Earth

Mineral Identification• Each mineral has unique properties that can be

used to identify it.1. Color: the easiest test to do on a mineral, but the

least reliable.

Amethyst

Rose QuartzCitrine

Calcite

Halite

Corundum

Quartz

Mineral Identification2. Streak: the color of the powdered mineral• Obtained by rubbing the unknown mineral on a

streak plate (porcelain tile).

The mineral Hematite ALWAYS has a red streak

One way to tell Fool’s Gold apart from real Gold is by their STREAK.

Real gold has a golden streak

Pyrite has a black or dark green streak

Mineral Identification3. Luster: The shine from an unweathered mineral’s

surface–Metallic – shines like a polished piece of metal. –Non-metallic – does NOT shine like a metal.

Glassy luster in Quartz

Pearly luster in Muscovite

Earthy luster in Hematite

Metallic luster in Pyrite

Metallic luster in Galena

Mineral Identification4. Hardness: a mineral’s

resistance to scratching

The hardness of some common items:•Fingernail – 2.5•A Penny – 3.5•Glass – 5.5•A Streak Plate – 6.5

Mineral Identification5. Specific Gravity: the density of a mineral

compared to the density of water.

The mineral Galena has a high specific gravity

Mineral Identification6. Cleavage: the tendency of a mineral to break

along the zones of weakness• Minerals can have one, two, or several cleavage planes

Mica has ONE cleavage plane

Feldspar has TWO cleavage planes

Halite (salt) has THREE cleavage

planes

7. Fracture: a mineral may break along uneven surfaces.

• Mineral has no preferred zones of weakness.

Splintery fracture in Hornblende

Conchoidal fracture in Quartz

Mineral Identification

8. Crystal Structure: orderly arrangement of the atoms in the mineral• The geometric shape of a mineral can reflect its

crystal structure.

Mineral Identification

Herkimer Diamonds are quartz crystals that have a unique 18-sided geometric shape.

Other Ways to Identify Minerals• Acid – Calcite will fizz in weak hydrochloric acid (HCl)

• Magnetism – Magnetite will pick up paper clips / staples.

• Taste – Halite is rock salt and will taste salty.

• Fluorescence – some minerals (mostly forms of calcite) will glow in fluorescent colors under a black (UV) light.

• Double refraction – some clear forms of calcite will make a double image of words.

Fluorescence of Minerals

Double Refraction