Minerals identification 4 1

 Particles of the mineral line up in a pattern that repeats. The repeating pattern of the minerals particles forms a solid called a crystal  Faces – are flats sides of the crystal t

Section 1: Properties of

Minerals

 What is a mineral?

 mineral – A naturally occurring, inorganic solid that has a crystal

structure and a definite chemical composition.

 A substance must have all 5 characteristics to be classified as a mineral.

A mineral must be/have:

 The substance must be formed

by processes that occur naturally

in the world

Example: quartz

Forms naturally when magma

cools and hardens deep beneath the Earth’s surface

 Materials such as cement, plastic, brick, steel, and glass all come from substances found in Earth’s crust but they are manufactured by people.

 Inorganic – the mineral cannot arise from materials that were once part of a living thing

 Ex Coal is NOT a mineral because it is made up the remains of plants and animals

 A mineral is always solid

 Has a definite volume and shape.

 Particles that make up a solid are tightly packed together, therefore they move very little

(compared to the particles of a liquid)

 Particles of the mineral line up in a pattern that repeats.

 The repeating pattern of the minerals particles forms a solid

called a crystal

 Faces – are flats sides of the crystal

that meet at sharp edges and

corners

 Element – a substance composed of a single kind of atom

 Ex Hydrogen

 Compound – Two or more elements combined so that the elements no longer have distinct properties

 Ex Water H 2 0

 Minerals always contain certain elements in definite proportions; most minerals are compounds

example: Quartz

SiO2

One element of silicon, 2 elements of oxygen

 Compounds have their own unique properties that differ from the

properties of the elements that form it.

 Some elements that occur in nature, in pure form, that are minerals include:

(Cu)

 Geologists have identified about 3,800 minerals

 Each mineral has characteristic properties that can be used to identify it.

 Some properties can be determined by looking at it, some properties require testing

 An easily observed physical property.

 Color alone is not enough to make an identification.

 Ex Gold, pyrite and chalcopyrite = gold color

 Only a few minerals can be identified using color only.

 Ex Malachite- always green, azurite – always blue.

 The streak of a mineral is the color of its powder

 The streak color and the mineral color are often different

 To test: rub a mineral against an unglazed tile (streak plate)

 Luster – used to describe how a mineral reflects light from its surface.

 Minerals containing metals are often shiny.

 Other terms to describe luster - Earthy, waxy, and pearly.

 Each mineral has a characteristic Density.

 Density – the mass in a given space or mass per unit volume.

 Density = mass (g)

volume (cm 3 )

 Displacement – the volume of the displaced water equals the volume of the sample

 To calculate the density of a mineral, divide the mass of the mineral sample by its volume.

 Density = Mass/Volume

 For example, if a sample of olivine has a mass of 237 g and a volume

of 72 cm3, then the density is

 237 g/72 cm3 = 3.3 g/cm3

- Properties of Minerals

 Take a few minutes to work through the following problem with a partner.

A sample of calcite has a mass of 324 g and a volume of 120 cm3 What is its density?

324 g ÷ 120 cm3 = 2.7 g/cm3

 Take a few minutes to work through the following problem with a partner.

 Predicting:

A piece of pyrite has a volume of 40 cm 3 What is its mass?

- Properties of Minerals

200 g

 Take a few minutes to work through the following problem with a partner.

1. What is the mass of sample B? What is the volume

of sample B?

2. What is the density of Sample B?

3. What is the mass of Sample C? What is the volume

of Sample C?

4. What is the density of Sample C?

5. Compare the density of Sample B to that of Sample

C?

 Friedrich Mohs – An Austrian mineral expert.

 In 1812 invented a test to describe the hardness of minerals.

 Called the Mohs hardness scale

 This scale ranks minerals from softest to hardest

 A scratch test is used, a mineral can scratch any mineral softer than itself, but can be scratched by any mineral that is harder.

 The crystals of each mineral grow atom by atom to form the minerals crystal structure.

 Geologists classify these structures into 6 groups based on the number and angle of the crystal faces

 These groups are called crystal systems.

 Example- Halite crystals are cubic Halite crystals have 6 square faces that meet at right angles forming a perfect cube.

- Properties of Minerals

Identifying Property – Crystal Systems

 Cleavage – a property of a mineral that causes it to split easily along flat surfaces.

 Determined by the arrangement of atoms in its crystals.

 The arrangement of the atoms in the mineral causes the crystal to break apart more easily in one direction than another.

direction, forming flat sheets Feldspar is

another mineral that has cleavage.

 Fracture – describes how a mineral looks when it breaks apart in an irregular way

evenly.

 Geologist use a variety of terms to describe

fracture

produces curved, shell like surfaces that

look like chipped glass.

 Pure metals like copper and iron form

jagged points - hackly (jagged) fracture

 soft minerals that crumble - earthy fracture

 Minerals that form rough, irregular

surfaces - uneven fracture

Conchoidal Fracture

 Smooth and curved (called clam shell too)

Quartz (SiO2 , Silicon dioxide )

Subconchoidal Fracture

 Subconchoidal: Smooth and but not curved

Andalusite (Al2 SiO5, Aluminum Silicate )

Uneven Fracture

 Common Type

Anhydrite (CaSO4, Calcium Sulfate )

Jagged Fracture

 Sharp points in edges that catch on the finger when rubbed across

Copper (Cu, Elemental Copper )

Earthy Fracture

 Produces a texture similar to broken children's clay

Limonite (A mixture of hydrated iron oxides)

 Some minerals can be identified by special physical properties.

 Examples:

 Magnetism

 Occurs naturally in a few minerals: Magnetite

 Fluorescence (glows under ultraviolet light)

 Scheelite

 Reactivity – reacts chemically to acids

 Aragonite and calcite

 Optical properties – bends light to produce double image

 Calcite

 Radioactivity – the process that occurs when a nucleus decays and emits alpha, beta or gamma radiation.

Special Properties

 Fluorescence: minerals that glow in ultraviolet light

Scheelite (CaWO4, Calcium

Tungstate ) Under ultraviolet

Special Properties

 Magnetism: Acts like a magnet

Magnetite (Fe3O4, Iron Oxide )

Special Properties

 Electrical

Quartz (SiO2 , Silicon dioxide)

Special Properties

 Radioactive

Uraninite (UO2 , Uranium Oxide)