Kristalografi dan MineralogiKristalografi dan Mineralogi

Dikompilasi oleh Dr. I Wayan WarmadaLab Bahan Galian, Jurusan Teknik Geologi, FT-UGM

URL: http://warmada.staff.ugm.ac.id/ Twitter: @warmada

1-PengantarVer. 1.2/20131029

What is a mineral?What is a mineral?

What are the characteristics of all What are the characteristics of all minerals?minerals?

1. A mineral occurs naturally.1. A mineral occurs naturally.

2. A mineral is solid.2. A mineral is solid.

3. A mineral has a definite chemical 3. A mineral has a definite chemical composition.composition.

4. A mineral’s atoms are arranged in a 4. A mineral’s atoms are arranged in a repeating pattern. repeating pattern.

((What vocabulary term do you think of when you hear this?)What vocabulary term do you think of when you hear this?)

5. A mineral is inorganic (was never 5. A mineral is inorganic (was never alive)alive)

Is Coal a Mineral?Is Coal a Mineral? We burn coal as a source of energy. It pollutes We burn coal as a source of energy. It pollutes

the air when burned.the air when burned. Is coal considered a mineral?Is coal considered a mineral?

Is Coal a Mineral?Is Coal a Mineral?

Miners refer to coal as a “mineral resource” Miners refer to coal as a “mineral resource” because it is removed from the ground.because it is removed from the ground.

Is Coal a Mineral?Is Coal a Mineral?

But is it But is it reallyreally a mineral? a mineral? (hint: look at the formation of coal and decide; keep the (hint: look at the formation of coal and decide; keep the

characteristics of a mineral in mind)characteristics of a mineral in mind)

Coal Coal

Coal is referred to as a “mineral resource”Coal is referred to as a “mineral resource” Coal is not really a mineral because it formed from Coal is not really a mineral because it formed from

once-living organismsonce-living organisms Coal formed from Coal formed from swamp plantsswamp plants It takes millions of years for coal to form; this makes it It takes millions of years for coal to form; this makes it

a nonrenewable resourcea nonrenewable resource Coal is a very important part of Virginia’s economyCoal is a very important part of Virginia’s economy Coal is found predominantly in the Coal is found predominantly in the Appalachian PlateauAppalachian Plateau

physiographic provincephysiographic province

Mineral Composition & Mineral Composition & GroupsGroups

Of the almost 4000 known minerals, Of the almost 4000 known minerals, only about 30 are common.only about 30 are common.

The most common are quartz, feldspar, The most common are quartz, feldspar, mica, and calcite.mica, and calcite.

MineralsMinerals

Quartz and feldspar are the 2 most abundant Quartz and feldspar are the 2 most abundant rock-forming minerals in the Earth’s crustrock-forming minerals in the Earth’s crust

In fact, over In fact, over 60%60% of the Earth’s crust is of the Earth’s crust is made up of the family of minerals made up of the family of minerals

known as feldspar!known as feldspar!

In fact, over In fact, over 60%60% of the Earth’s crust is of the Earth’s crust is made up of the family of minerals made up of the family of minerals

known as feldspar!known as feldspar!

These minerals make up most of the These minerals make up most of the rocks found in the Earth’s crust.rocks found in the Earth’s crust.

Earth’s CrustEarth’s Crust

Earth’s crust is made up of 90 elements.Earth’s crust is made up of 90 elements. 98% of the crust is made up of only 8 elements98% of the crust is made up of only 8 elements

Earth’s CrustEarth’s Crust

The eight most abundant elements in Earth’s The eight most abundant elements in Earth’s crust are as follows:crust are as follows:

oxygen(O), silicon(Si), aluminum(Al), iron(Fe), oxygen(O), silicon(Si), aluminum(Al), iron(Fe), calcium(Ca), sodium(Na), potassium(K), & calcium(Ca), sodium(Na), potassium(K), & magnesium(Mg)magnesium(Mg)

Mineral CompositionMineral Composition

Minerals are made up of elements found in the Minerals are made up of elements found in the Earth’s crustEarth’s crust

Minerals are in groups based on the elements Minerals are in groups based on the elements contained in themcontained in them

Mineral GroupsMineral Groups Major groups of minerals are as follows:Major groups of minerals are as follows:

1. Silicates 1. Silicates 2. carbonates 2. carbonates 3.oxides 3.oxides 4. sulfides 4. sulfides 5. sulfates5. sulfates

6.halides6.halides 7. hydroxides 7. hydroxides 8. phosphates 8. phosphates 9. native 9. native

elementselements

SilicatesSilicates

The The silicatessilicates are the largest group of rock- are the largest group of rock-forming mineralsforming minerals

SilicatesSilicates contain both contain both silicon & oxygensilicon & oxygen and one and one or more other elementsor more other elements

Silicon and oxygen are the 2 most abundant Silicon and oxygen are the 2 most abundant elements in the Earth’s crustelements in the Earth’s crust

Pictured:AgatePictured:Agate

To be able to identify these and other To be able to identify these and other minerals, we need to look at the minerals, we need to look at the properties properties used to separate and used to separate and

distinguish these minerals.distinguish these minerals.

Identifying MineralsIdentifying Minerals

Remember!:Remember!:

Rarely is a mineral identified by a Rarely is a mineral identified by a single property.single property.

These properties need to be These properties need to be considered together to correctly considered together to correctly

identify a mineral.identify a mineral.

Physical PropertiesPhysical Properties

►ColorColor►LusterLuster►StreakStreak►HardnessHardness►Specific GravitySpecific Gravity

Color is the most easily observed Color is the most easily observed mineral property and the mineral property and the leastleast

useful! useful!

Some exceptions to the color rule would Some exceptions to the color rule would be be cinnabarcinnabar, which is always , which is always redred, , sulfursulfur, which is bright , which is bright yellowyellow, and , and

malachitemalachite, which is , which is greengreen..

Many minerals have a similar color.Many minerals have a similar color.

Many minerals can turn colors due to Many minerals can turn colors due to impurities, or they can change impurities, or they can change

colors in various circumstances.colors in various circumstances.

For example, pure quartz is colorless For example, pure quartz is colorless or white, impurities can make the or white, impurities can make the

mineral rose, purple or pink!mineral rose, purple or pink!

Discuss the following!Discuss the following!

Can you name the 5 characteristics Can you name the 5 characteristics of minerals?of minerals?

Why isn’t color a very good property Why isn’t color a very good property to identify most minerals?to identify most minerals?

Luster refers to how light is reflected Luster refers to how light is reflected from a mineral. Notice the from a mineral. Notice the

difference between these two difference between these two minerals.minerals.

The mineral on the left has a The mineral on the left has a metallic metallic lusterluster, and the one on the right, a , and the one on the right, a

nonmetallic lusternonmetallic luster..

Terms used to describe nonmetallic Terms used to describe nonmetallic luster:luster:

Dull, pearly, silky, glassy, and brilliantDull, pearly, silky, glassy, and brilliant

StreakStreak of a mineral is the color of its of a mineral is the color of its powder when rubbed on a streak plate powder when rubbed on a streak plate

or an unglazed porcelain tile.or an unglazed porcelain tile.

The streak is often not the same color as The streak is often not the same color as the mineral. the mineral.

A minerals color may vary, but the A minerals color may vary, but the streak rarely will!streak rarely will!

StreakStreak

For example, both gold and pyrite look alike. For example, both gold and pyrite look alike. They appear to be the same thing.They appear to be the same thing.

If you do the streak test, you will discover that If you do the streak test, you will discover that goldgold leaves a yellow streak, whereas pyrite leaves a yellow streak, whereas pyrite leaves a greenish-black or brown-black streak.leaves a greenish-black or brown-black streak.

PyritePyrite is known as is known as “fool’s gold”“fool’s gold” because it looks because it looks like gold, but is notlike gold, but is not

Gold & PyriteGold & Pyrite

The The cleavage cleavage of a mineral is its tendency of a mineral is its tendency to split easily or to separate along flat to split easily or to separate along flat

surfaces.surfaces.

Cleavage can even be observed on tiny Cleavage can even be observed on tiny mineral grains making it a very useful mineral grains making it a very useful

property!property!

FeldsparFeldspar splits readily in two directions, splits readily in two directions, always at or near right angles.always at or near right angles.

CalciteCalcite andand galenagalena cleave in three directions.cleave in three directions.

They are said to have three good cleavages.They are said to have three good cleavages.

Not all minerals show cleavage.Not all minerals show cleavage.

Those that break with jagged edges are said Those that break with jagged edges are said to haveto have fracturefracture..

HardnessHardness of a mineral is how easily the of a mineral is how easily the mineral can be scratched.mineral can be scratched.

Friedrich Friedrich MohsMohs devised a hardness devised a hardness scale that we refer to as Mohs scale that we refer to as Mohs

Hardness Scale.Hardness Scale. In this scale, 10 well-known minerals In this scale, 10 well-known minerals

are given numbers from 1-10.are given numbers from 1-10. Talc is the softest mineral and a Talc is the softest mineral and a

diamond is the hardest mineraldiamond is the hardest mineral

MineralMineral SoftnessSoftness

TalcTalc 11

GypsumGypsum 22

CalciteCalcite 33

FlouriteFlourite 44

ApatiteApatite 55

FeldsparFeldspar 66

QuartzQuartz 77

TopazTopaz 88

CorundumCorundum 99

DiamondDiamond 1010

Common Common ObjectsObjects

HardnessHardness

FingernailFingernail 2.52.5

PennyPenny 3.53.5

NailNail 4.54.5

GlassGlass 5.55.5

Steel FileSteel File 6.56.5

Streak Streak PlatePlate

77

Common objects are used to test the hardness of Common objects are used to test the hardness of mineralsminerals

Example-Example-CalciteCalcite has a hardness of 3 and a copper has a hardness of 3 and a copper

penny just scratches it because it has a penny just scratches it because it has a hardness of 3.5hardness of 3.5

Example:Example:

ApatiteApatite has a hardness of 5 and can be scratched has a hardness of 5 and can be scratched by a steel knife blade.by a steel knife blade.

ExampleExampleQuartzQuartz, with a hardness of 7, is the hardest , with a hardness of 7, is the hardest

of the common minerals. It easily of the common minerals. It easily scratches hard glass. Quartz is also scratches hard glass. Quartz is also

similar in composition to glass.similar in composition to glass.

Gems Gems are known for their extreme are known for their extreme hardness.hardness.

Crystal shapeCrystal shape can be a useful property to can be a useful property to identify minerals if the minerals have identify minerals if the minerals have

had the time and space to form had the time and space to form crystals. Most mineral grains that are crystals. Most mineral grains that are found in rocks, lack the room to grow.found in rocks, lack the room to grow.

Specific gravitySpecific gravity tells you how many tells you how many times as dense as water the mineral is.times as dense as water the mineral is.

Pure gold can have a specific gravity as Pure gold can have a specific gravity as high as 19.3!high as 19.3!

CalciteCalcite is calcium carbonate, CaCO is calcium carbonate, CaCO33. If a . If a drop of weak hydrochloric acid is drop of weak hydrochloric acid is

placed on calcite, the acid bubbles as placed on calcite, the acid bubbles as carbon dioxide is released.carbon dioxide is released.

Malleable

Magnetic

Radioactive

Flourescence

Taste

Some minerals that Some minerals that contain iron, are contain iron, are

magnetic and can be magnetic and can be picked up by a picked up by a

magnet. Magnetite magnet. Magnetite is an example of a is an example of a magnetic mineral.magnetic mineral.

This is the state of This is the state of glowing while under glowing while under

a ultraviolet light.a ultraviolet light.

Some minerals even Some minerals even glow once the light glow once the light

is turned off!is turned off!

Some minerals, such Some minerals, such as thisas this uraniniteuraninite, are , are

radioactive.radioactive.

They give off They give off subatomic particles subatomic particles that will activate athat will activate a

Geiger counterGeiger counter..

HaliteHalite (rock salt) (rock salt) can be identified can be identified

by its taste.by its taste.

This practice is not This practice is not recommended!recommended!

Special PropertiesSpecial PropertiesOf MineralsOf Minerals

Special PropertiesSpecial Properties

Magnetite is magnetic; lodestone is a type of Magnetite is magnetic; lodestone is a type of magnetitemagnetite

Calcite fizzes when you put hydrochloric acid on Calcite fizzes when you put hydrochloric acid on itit

When you look through calcite, you can see a When you look through calcite, you can see a double imagedouble image

Sulfur can be identified by its bright yellow Sulfur can be identified by its bright yellow color and bad smellcolor and bad smell

GemsGems

Highly prized because they are rare and beautifulHighly prized because they are rare and beautiful Can be cut and polished and used for jewelryCan be cut and polished and used for jewelry The brighter and more colorful samples are cut and The brighter and more colorful samples are cut and

polishedpolished Example: amethyst- a form of quartz which has Example: amethyst- a form of quartz which has

manganese in it to give it its purple colormanganese in it to give it its purple color Gems are very hardGems are very hard

OresOres

A mineral that is A mineral that is UsefulUseful & & ProfitableProfitable Waste rock must be removed to get to the desired Waste rock must be removed to get to the desired

mineral; removing waste rock is very expensive.mineral; removing waste rock is very expensive. The value of a mineral can change if the supply The value of a mineral can change if the supply

of or demand for that mineral changesof or demand for that mineral changes

Ores & Their UsesOres & Their Uses

Examples:Examples:

Bauxite- aluminumBauxite- aluminum Hematite- ironHematite- iron Galena- leadGalena- lead Halite- rock saltHalite- rock salt Graphite- pencil “leadsGraphite- pencil “leads Magnetite- ironMagnetite- iron