Minerals

This is not a spider web. It is a fractal; a repeating

geometric design

What is a mineral

• A mineral is a natural, inorganic, crystalline solid• Ask these questions:

– Is it inorganic? • Only inorganic materials can be minerals

– Organic means it is or was once alive– Coal is made from dead plants and is organic

– Does it occur naturally?• Steel is man-made and is not a mineral

– Does it have a crystalline form?• Petroleum occurs naturally and is inorganic but is not a solid so

it has no crystalline form and is not a mineral– Does it have a definite chemical composition?

• Mixtures are not minerals; compounds can be minerals

Rocks and the Rock Cycle

•Made of one or more types of minerals

Types of Minerals

• The most common minerals are rock-forming

• All minerals fall into two categories:– Silicate minerals

– Non-silicate minerals

Silicate Minerals• All silicate minerals contain silicon

(Si) and Oxygen (O) in varying combinations– Quartz contains only Si and O

• Feldspar is the most common silicate mineral– Different types of Feldspar are formed

when other elements (K, Na, Ca, etc) are combined with the Si and O

• Feldspar and quartz make up 50% of the earth’s crust

• Silicate minerals make up 96% of the Earth’s crust

Non-silicate Minerals

• Only 4% of the Earth’s crust

Crystalline structure

• A crystal is a natural solid with a definite shape– A large mineral crystal will display the

characteristic geometry of its crystalline structure

– Crystals have a specific geometry of atoms that repeats

– If a mineral is allowed to develop unrestricted then it will form one, huge crystal

Crystal Shapes

• Draw Figure 3 on page 107

Mineral identification

• A Mineralogist is a scientist who identifies minerals• Characteristics:

– Color

– Luster

– Streak

– Cleavage/fracture– Hardness– Crystal shape– Density

Color

• This is probably the worst characteristic to classify minerals because it is inconsistent– Some minerals have distinctive colors (Sulfur is yellow,

azurite is blue, serpentine is green)– Many minerals are similar in color

Color

– Very small amounts of certain element can greatly affect the color

• Corundum is a colorless mineral made from Aluminum and Oxygen but with a little bit of chromium it forms a ruby

• Sapphire is corundum with traces of cobalt and titanium• Amethyst is quartz that has a purple color because of small

amount of Manganese and Iron

Streak• The color of the mineral

in its powdered form is called the streak– This is fairly reliable for

identification

• Metallic minerals have a dark streak– Ex. Pyrite (fool’s gold) has

a black streak

• Nonmetallic minerals have a streak that is colorless or a very light shade of the mineral’s normal color

Cleavage and Fracture

• Cleavage: when a mineral splits evenly along flat surfaces– Ex. Micas which split in sheets– The cleavage runs parallel to a plane in the crystal

where the bonding is weak– Fracture: when a mineral breaks unevenly

• Curved surfaces are called conchoidal• Fibrous surfaces look like broken wood• Rough surfaces are called uneven or irregular

Hardness

• Hardness is the ability of a mineral to resist scratching– Ex. A diamond is extremely hard but can easily

be split along cleavage planes– The hardness of an unknown mineral can be

determined by scratching it against other minerals of a known hardness on the Mohs hardness scale

– The hardness of the mineral determines the strength of the bonds between the atoms

• Graphite and diamonds are made from carbon. Graphite has no crystal structure so it is not as hard as diamonds

Hardness

• The Moh’s scale is used to determine relative hardness

• It has hardness values from 1 (softest) to 10 (hardest) with examples of each value

• You can classify the hardness of a mineral by determining whether or not it will scratch a mineral with a known value.– If it will scratch the other mineral, its Moh’s scale

value is larger than that mineral– If it will NOT scratch the other mineral, its Moh’s

scale value is smaller than that mineral

Crystal Shape

• A certain mineral always has the same general shape because the atoms or ions that form its crystals always combine in the same geometric pattern

Density

• Density = Mass ÷ Volume

• The density depends on what type of atoms the mineral contains and how closely they are packed together– Most of the common

minerals have densities between 2 and 3 g/cm3

– Heavy metals (gold, uranium, lead) can have densities from 7 to 20 g/cm3

Special Properties• Magnetism

– Magnetite is the most common• Lodestone is a type of magnetite

that acts like a magnet

• Double Refraction– Clear minerals still fracture light

that passes through them creating double images

• Radioactivity– Some atoms have unstable

protons and neutrons. This nuclear decay releases energy

• Uranium and Radium are some radioactive elements that occur in minerals

• Pitchblende is the most common uranium containing mineral

Special Properties

• Fluorescence (ability to glow under UV light)– Calcite is white under normal light but red under

UV light– Fluorescent minerals absorb UV light and then

produce visible light of various colors

• Phosphorescence (ability to glow under UV light even after UV light is shut off)

Classwork 1 – Minerals and Rocks

1. Define mineral

2. R___ are made of m____

3. Name the two types of minerals. Which one is most prevalent on Earth?

4. Name and describe six properties of minerals that can be used to identify them

5. Name and describe two special properties of minerals

6. Is steel a mineral? Explain.

Copy the questions into your notebook (right-side) and answer them