CHAPTER 2 MINERALS

Group Presentation Notes

DEFINITION OF A MINERAL

A mineral is naturally occurring, inorganic

solid with an orderly crystalline structure

and a definite chemical composition.

CHARACTERISTICS

1. Naturally occurring – minerals form by

natural geologic processes; not man made

2. Solid substance – exists as a solid on

Earth’s surface

CHARACTERISTICS

3. Orderly crystalline structure – atoms

are arranged is an organized pattern, which

affects their crystal shape (internal

structure)

CHARACTERISTICS

4. Definite chemical composition – most minerals

are chemical compounds of two or more

elements.

5. Generally considered inorganic – most minerals

are inorganic crystalline solids found in nature, like

halite (table salt).

WAYS THAT MINERALS FORM

1. Crystallization from Magma – as

magma cools, elements combine to form

minerals

• Examples: Quartz, Muscovite, Feldspar

WAYS THAT MINERALS FORM

2. Precipitation – as water evaporates, the

dissolved substances in the water can react

to form minerals

• Examples: Calcite and Halite

(limestone caves are formed by this same process)

WAYS THAT MINERALS FORM

3. Pressure and Temperature – an increase in

pressure and/or temperature can cause minerals

to become unstable and recrystallize (atoms

rearranged) to form new minerals.

• Examples: talc and muscovite

WAYS THAT MINERALS FORM

4. Hydrothermal Solutions – is a very hot mixture of

water and dissolves substances. When existing minerals

come in contact, chemical reactions can take place to

form new minerals. When solution cools dissolved

substances combine to form minerals.

• Examples: Bornite, chalcopyrite, quartz, and pyrite

HOW GROUPED?

Common minerals, together with the

thousands of others that form on Earth, can

be classified into groups based on their

composition.

SILICATES

Silicon (Si) and oxygen (O) combine to form a

structure called the silicon-oxygen tetrahedron.

This tetrahedron can join in a variety of ways

affecting the crystal shape.

• Example: Quartz, micas, augite & hornblende

CARBONATES

Minerals that contain the elements carbon

(C), oxygen (O) and one or more other

metallic elements.

• Examples: Calcite (CaCO3) and Dolomite

OXIDES

Minerals that contain Oxygen and one or

more other elements, which are usually

metals.

• Examples: Corundum (Al2O3) &

Hematite (Fe2O3)

SULFATES AND SULFIDES

Minerals that contain the element sulfur.

• Examples: Anhydrite, Gypsum, Galena,

Sphalerite, and Pyrite.

HALIDES

Minerals that contain a halogen ion plus

one or more other elements.

• Examples: Halite (NaCl) & Fluorite (CaF2)

NATIVE ELEMENTS

A group of minerals that exist in relatively

pure form.

• Examples: Gold (Au), Silver (Ag),

Copper (Cu), Sulfur (S), and

Carbon (diamond & graphite)

Properties of Minerals

COLOR

Unique to some minerals, while others will come

in many different colors and several different

minerals can come in the same color. Color of

minerals come from the elements.

• Example: Copper and Aluminum give turquoise its blue-green color

STREAK

The color of a mineral in its powdered form.

Obtained by rubbing a mineral across a streak plate

(little piece of unglazed tile). Color of the streak does

not vary from sample to sample in the same mineral.

• Example: Hematite has a distinctive red-brown

streak

LUSTER

Used to describe how light is reflected

from the surface of a mineral.

Different types of luster:

• Metallic, nonmetallic, glassy, pearly, silky,

earthy and brillant

CRYSTAL FORM

The visible expression of a mineral’s internal

arrangement of atoms.

When a mineral forms slowly and without

space restrictions, it will develop into a crystal

with well-formed faces

HARDNESS

A measure of the resistance of a mineral to being

scratched

One of the most useful properties in identifying

minerals

Standard hardness scale called the Mohs scale consists

of 10 minerals arranged from 10 (hardest) to 1 (softest)

CLEAVAGE

The tendency of a mineral to cleave, or

break, along flat even surfaces.

• Example: Mica cleaves to form flat sheets

FRACTURE

The uneven breakage of a mineral.

• Example: Quartz has a curvy fracture

called conchoidal fracture.

DENSITY

A property of all matter that is the ratio

of an object’s mass to its volume.

• Example: Density of Galena is 7.5g/cm3

DISTINCTIVE PROPERTIES

Distinctive feels: talc feels soapy and graphite feels greasy

Some metallic minerals are easily shaped

Some minerals like magnetite are magnetic

Double refraction: calcite makes printed material appear double

Carbonate minerals react with acid (HCl) – fizz and bubble

Smell: sulfur smells of rotten eggs