What is a mineral?

• A mineral is a (1)naturally occurring (2)inorganic, (3)solid with a (4)definite chemical composition and (5)crystalline structure.

• There are over 4000 known minerals, but only about 20 are common.

What is a mineral? (cont.)

• Minerals can either be a made of a pure substance – a single element (gold, silver, lead, iron)

BUT Most minerals are compounds• The same elements are found in most

minerals – they are called mineral forming elements:–Oxygen; Silicon; Aluminum; Iron;

Calcium; Sodium; Potassium; Magnesium

How do minerals form?

Minerals can form several ways:1. From molten rock/magma 2. Due to intense heat and

pressure3. Evaporation4. Chemical Action

What are silicates?

• Minerals are classified into 2-groups based on their composition:

1. Silicate Minerals 2. Nonsilicate Minerals

Silicate Minerals• Are minerals made of the 2 most

abundant elements in Earth’s crust – silicon (Si) and oxygen (O)

• A silicate may also contain one or more metallic elements like aluminum or iron

• There are a few silicates that do not contain metals – like quartz

• More that 90% of the minerals in Earth’s crust are silicates

• Examples – feldspars, quartz, hornblende, olivine, muscovite, biotite

Nonsilicate Minerals Groups

1. Carbonates – metal + C + O2. Halides – metal + halogen3. Native elements – single element4. Oxides – Metal + O5. Sulfates – S + metal + O6. Sulfides – S + metal

How To Identify Minerals Based on

Properties

quartzselenium

calcite

quartz

Color

Color• First thing noticed • Not useful property to identify minerals because:

– One mineral can have different colors– Different minerals can have the same color

• However some minerals do have a distinct color. Examples: sulfur, malachite, cinnabar.

Crystal Shape

• Arrangement of its component atoms and/or ions• Responsible for the outward shape of the crystal• Crystal system affects a number of other

properties such as cleavage, density, and hardness

Luster

• The way light reflects off the surface of a mineral• How you would tell someone how a mineral looks• Nothing to do with color or shape • Terms used are generally not scientific, but are

meant to be descriptive

Hardness

• A good physical property in mineral identification • Measure of the strength of the structure of the

mineral relative to the strength of its chemical bonds --- Stronger bonds = greater hardness

• Hardness can be tested through scratching• A mineral can only be scratched by a harder

substance

Streak

• Color of the powder of a mineral• To test for streak, rub a mineral across a tile of

white unglazed porcelain and examine the color of the "streak" left behind

• Two minerals that have similar outward color may have different colors when powdered.

hematite galena

Cleavage

• Cleavage is a smooth break producing what appears to be a flat crystal surface that can be broken along the same parallel plane over and over again

• Terms are: perfect, imperfect, good, distinct, indistinct, and poor.

biotite

• Fracture is a description of the way a mineral tends to break

• The surface that can be described as Smooth, Irregular, Jagged, Splintery

• Most common fracture type is conchoidal which is a smoothly curved fracture that looks like broken glass

Fracture

Specific Gravity

• Compares the density of a mineral to the density of water

• If a mineral has a SG of 2, then it is twice as dense as water

• If a mineral has a SG of 3 then it is three times as dense as water and so forth.

Additional Mineral Properties

Acid Test

• Carbonate minerals (calcite & dolomite) tend to react to acids

• The reaction is written as follows for calcite, the mineral for which this test is made famous:

CaCO3 + 2H(+1) -------> Ca(+2) + H2O + CO2 (gas)

The Fluorescence Minerals

• Light from these ultraviolet lamps reacts with the chemicals of a mineral and causes the mineral to glow; this is called fluorescence.

Examples:• Fluorite• Calcite• Autunite• Willimite

Magnetism

• Magnetite is a natural magnet, which is a good way to identify it from other metallic mineral ores.

Taste

• Most commonly "tasted" mineral is halite/rock salt

• YOU should never do this because there are minerals that are poisonous

• Some solubility in water is required in order to have a taste

The Scent of a Mineral

• The most renowned smelly mineral is sulfur

• Marcasite gives off a noticeable sulfur-like odor when it decomposes

• Arsenic minerals tend to have a garlic scent as is consistent with the element and poison arsenic

• Clay minerals have a clay-like smell that is sometimes called earthy