Minerals

MineralsMinerals

Dr. R. B. SchultzDr. R. B. Schultz

What is the difference between a mineral and a rock?What is the difference between a mineral and a rock?

The earth is made of rocks, which are in turn made of minerals. Minerals are the “building blocks” of rocks.In order for something to be classified as a mineralmineral, it must meet five (5) criterion:Minerals are:

Naturally occurring, Inorganic, Have known chemical compositions, Have definite physical properties,Are solid at room temperatures for long periods of time They are usually (although not always) crystalline.

How are minerals classified?How are minerals classified?

Minerals are classified based on:chemical composition (what elements they are composed of)crystal structure (how the elements are arranged)

Minerals are made of different ionsions bonded together. Ions are charged particlesCations are positively charged (example: Na+1)Anions are negatively charged (example Cl–1)Common ions in earth's crust:O - most common ion (anion) Si, Al, Fe, Ca, Na, K, Mg, (Cations) Minerals are made mainly of these ions

How are minerals structured microscopically?How are minerals structured microscopically?Crystal structure depends on sizes of and charges on ionsMost common mineral group is the silicatessilicatesThe crust and mantle of the Earth make up about 80% The crust and mantle of the Earth make up about 80% of the volume of the planet and are predominantly of the volume of the planet and are predominantly made of silicates.made of silicates.All silicate minerals contain silicon (Si) and oxygen (O)MaficMafic silicate minerals contain iron and magnesium and are dark in color

Examples: olivine, pyroxene, amphibole, and biotite mica

Felsic Felsic silicates don't contain magnesium or iron, and are light in color

Examples: feldspar, quartz, clay minerals, muscovite mica

What are silicate minerals and what are they composed of?What are silicate minerals and what are they composed of?

Basic building block: silica tetrahedron Silica tetrahedron is a silicon ion bonded to 4 oxygen ions Silicon is positively charged (+4) Oxygen is negatively charged (-2) Net charge on tetrahedron: -4 Because entire tetrahedron is negatively charged, it is attracted to cations Tetrahedra may link together by a cation (e.g. Mg, Fe, Na, Ca, K) serving as a bridge, or may link together by sharing oxygens

Silica TetrahedronSilica Tetrahedron

What possible structures can be made with a silica tetrahedra? What possible structures can be made with a silica tetrahedra? Simple TetrahedraSimple TetrahedraCations serve as links between tetrahedra; no sharing of oxygens Examples: olivine, and garnet, (also mafic silicates)

Single chain silicatesSingle chain silicatesAdjacent tetrahedra form a chain by sharing 2 of their oxygens with neighboring tetrahedra Examples: pyroxenes, which also happen to be mafic silicates

Double chain silicatesDouble chain silicatesTwo chains can link up by sharing oxygens Examples: amphiboles, which are mafic silicates too

Sheet silicatesSheet silicatesSheets are formed when each tetrahedron shares 3 of its oxygens with its neighbors Examples: micas, biotite (mafic) and muscovite (non-mafic), and clay minerals, which are non-mafic silicates

Framework silicatesFramework silicatesEvery oxygen in each tetrahedron is shared to form 3-D framework Examples: feldspar, quartz, (also non-mafic)

Olivine: Isolated TetrahedraOlivine: Isolated Tetrahedra

Pyroxene: Single ChainPyroxene: Single Chain

Amphibole: Double ChainAmphibole: Double Chain

Micas: SheetsMicas: Sheets

Feldspars: Simple FrameworkFeldspars: Simple Framework

Quartz: Complex FrameworkQuartz: Complex Framework

What are What are NONNON--Silicate Minerals?Silicate Minerals?Minerals that do NOT contain Silicon and Oxygen as a tetrahderalstructure.Fluorite: used as a toothpaste additiveCalcite: calcium carbonate; limestone is made of calcite. Gypsum: calcium sulfate ; used for wall board (drywall)Galena: lead sulfide; mined for leadPyrite -- iron sulfide; mined for ironHalite -- sodium chloride (table salt); for your french fries

Fluorite Halite CalciteFluorite Halite Calcite

How does one identify a mineral?How does one identify a mineral?

Geologists determine the identity of an unknown mineral by describing its physical propertiesphysical properties. Each mineral has its own unique set of physical properties and characteristics.

Physical Properties include:LusterLuster refers to the light reflected off of the mineral and its overall quality. Minerals can be termed: glassy, opaque, transparent, shiny, or most commonly: metallic and non-metallic. One of the first determinations a geologist must make is whether the mineral in metallic or non-metallic.HabitHabit refers to the overall shape of the mineral. Mineral scientists (mineralogists) use terms like:

"equant" “elongate" or "platy"

Isolated tetrahedra & framework silicate minerals tend to be equant in habit; chain silicates tend to be elongate, sheet silicates are platy.

NonNon--metallic mineralmetallic mineral

Metallic mineralMetallic mineral

How does a mineral break and what are its characteristics?How does a mineral break and what are its characteristics?CleavageCleavage is the term applied to a mineral’s preferred orientation of breakage when it splits along smooth flat surfaces..These special breakage surfaces correspond to zones of weak bonding in the crystal structure. To describe cleavage, one must determine the number of unique cleavage planes (directions) and their angle with respect to each other (e.g. salt breaks into cubes, with cleavage in 3 directions, all at 90 degrees)An irregular break (no smooth surfaces) is termed fracturefracture.

NO cleavage:NO cleavage:fracturefracture

One plane of cleavageOne plane of cleavage

Three planes of cleavageThree planes of cleavage

So whatSo what’’s the difference between s the difference between ““cleavagecleavage”” and and ““fracturefracture””??

What is the hardness of a mineral?Pretty much what it says: the ability to resist abrasion or scratching.Harder minerals or objects will scratch softer minerals. Softer minerals or objects get scratched. Geologists rank minerals numerically according to hardness using the Moh's Hardness ScaleNote objects are 0.5’s and minerals are whole numbers.

Moh's Hardness Scale (Commit this to memory)1.01.0 TALCTALC2.02.0 GYPSUMGYPSUM2.5 FINGERNAIL2.5 FINGERNAIL3.0 3.0 CALCITECALCITE3.53.5 COPPER PENNYCOPPER PENNY4.04.0 FLUORITE (Note the spelling!)FLUORITE (Note the spelling!)5.0 5.0 APATITEAPATITE5.55.5 STEEL KNIFE BLADE/GLASS PLATESTEEL KNIFE BLADE/GLASS PLATE6.06.0 ORTHOCLASE FELDSPARORTHOCLASE FELDSPAR7.07.0 QUARTZQUARTZ8.08.0 TOPAZTOPAZ9.09.0 CORUNDUM (RUBY)CORUNDUM (RUBY)10.0 DIAMOND 10.0 DIAMOND

Is color important?Is color important?Not really!Minerals vary greatly in color and thus color is unreliable as a physical property in many minerals, e.g. quartz Some minerals come in just one color; color may be useful in their identification StreakStreakRefers to color of powder residue left by rubbing mineral against a streak plate (unglazed porcelain). Streak does not vary even if color does. Other PropertiesOther Properties

Some minerals are magnetic (i.e., magnetite)Some minerals effervesce ("fizz") in dilute acid (calcite)Galena has a high specific gravity (like density)

These are all varieties of the mineral quartz:These are all varieties of the mineral quartz:

Milky quartzMilky quartz

CitrineCitrine

AmethystAmethyst

Smoky quartzSmoky quartz Rose quartzRose quartz

Although they are all different colors, Although they are all different colors, their luster, hardness, fracture, streak, their luster, hardness, fracture, streak, and other properties are identical.and other properties are identical.

A good way to go about identifying the minerals is:A good way to go about identifying the minerals is:

First, determine the luster (either metallic or non-metallic).

If metallic: determine the streak color and hardness; go to appropriate identification table.

if non-metallic, determine fracture or cleavage and hardness; go to appropriate identification table

Use the mineral identification tables to eliminate what the minerals CANNOT be. Use process of elimination. Read descriptions carefully.

Do NOT try to memorize every physical property of each mineral.

Rather, know one or two diagnostic properties that will tell you the mineral name every time.

Example: galena always makes cubes, always is silver-grey and always is very heavy.

What will the mineral identification quiz consist of?What will the mineral identification quiz consist of?

1. Moh’s Hardness Scale: you will be given the numbers 1 through 10; you are to write the names of the minerals and objects next to their appropriate hardness according to those as defined by Moh’s Scale (see slide on Moh’s Hardness Scale).

2. You will be given five (5) mineral samples from those we have identified in class.

You will be asked:

Its hardness on Moh’s Scale (you are allowed to use the tools/objects)

Whether the mineral has cleavage or fracture

Is it a silicate or non-silicate?

What is the family name of the mineral? (Example: micas, feldspars, silicates, non-silicates)

What might a practical use be for the mineral? (paperweight or jewelry are NOT practical uses)

3. You may NOT use your notes or flow charts on the quiz. However, you will be provided with the names of all minerals studied.

Key TerminologyKey Terminology

Mineral Chemical compositionCrystalline structure IonsCation AnionSilicate MaficFelsic Silica tetrahedronSingle chain Double chainSheet silicate Framework silicateNon-silicate Physical propertiesHabit LusterStreak CleavageHardness Moh’s Hardness Scale