Section 1: Properties of Minerals Chapter 4: Minerals Section 1: Properties of Minerals

How are minerals identified? Key Concepts: What is a mineral? How are minerals identified?

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.

5 Characteristics of a Mineral A mineral must be/have: Naturally Occurring Inorganic Solid Crystal Structure Definite Chemical Composition

Naturally occurring means: 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.

NOT naturally occurring: 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 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

Solid 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)

Crystal Structure 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. QUICK REVIEW: What Is the Difference Between an Element and a Compound? 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 H20

Definite Chemical Composition 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.

Definite Chemical Composition Some elements that occur in nature, in pure form, that are minerals include: Gold (Au), Silver (Ag), Copper (Cu) Listed on the periodic table

Identifying Minerals 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.

Identifying Properties Color Streak Luster Density Hardness Crystal Systems Cleavage and fracture Special Properties

Identifying Property- Color 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.

Identifying Property - Streak 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)

Identifying Property - Luster 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.

Identifying Property - Density Each mineral has a characteristic Density. Density – the mass in a given space or mass per unit volume. Density = mass (g) volume (cm3) Displacement – the volume of the displaced water equals the volume of the sample

- Properties of Minerals Calculating Density 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

Stop and Think Take a few minutes to work through the following problem with a partner.

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

Answer 324 g ÷ 120 cm3 = 2.7 g/cm3

Stop and Think Take a few minutes to work through the following problem with a partner.

Mineral Density - Properties of Minerals Predicting: A piece of pyrite has a volume of 40 cm3. What is its mass?

Mineral Density 200 g

Stop and Think Take a few minutes to work through the following problem with a partner.

Analyzing Data What is the mass of sample B? What is the volume of sample B? What is the density of Sample B? What is the mass of Sample C? What is the volume of Sample C? What is the density of Sample C? Compare the density of Sample B to that of Sample C?

Answers 1) 50g and 10cm3 2) 5g/cm3 3) 100g and 20cm3 4) 5g/cm3 5) the density of samples B and C is the same.

Identifying Property - Hardness 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.

Identifying Property - Hardness

Identifying Property – Crystal Systems 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.

Identifying Property – Crystal Systems - Properties of Minerals Identifying Property – Crystal Systems

Crystal systems – cleavage and fracture 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. Example- Mica separates easily in only one direction, forming flat sheets. Feldspar is another mineral that has cleavage.

Cleavage

Crystal Systems – cleavage and fracture Fracture – describes how a mineral looks when it breaks apart in an irregular way. Most minerals do not split apart evenly.

Geologist use a variety of terms to describe fracture Examples: quartz has a shell shaped (conchoidal) fracture. When it breaks, it 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 )

Splintery Fracture Fibrous or finely needle shaped minerals and have a relatively stronger structure in one direction than the other two. Serpentine (Mg,Fe)3Si2O5(OH)4, Magnesium Iron Silicate Hydroxide Splintery Kyanite (Al2 SiO5, Aluminum Silicate Non-fibrous

Earthy Fracture Produces a texture similar to broken children's clay Limonite (A mixture of hydrated iron oxides)

Identifying Properties – Special Properties 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)

Special Properties Reactivity to acids Calcite (CaCO3, Calcium Carbonate )