Chapter 2 – Section 2 Chapter 2 – Section 2 Mineral IdentificationMineral Identification

Please open your book to page 36.Please open your book to page 36.Please take notes over the yellow slides!Please take notes over the yellow slides!

Identifying MineralsIdentifying Minerals• How do you recognize someone you

know? You may be able to identify them by their hair color, height, weight, facial features, etc.

• Individual minerals also have characteristics that distinguish one from another.

Physical PropertiesPhysical Properties

• Mineral Appearance & Color

• Hardness

• Luster

• Specific Gravity

• Streak

• Cleavage and Fracture

Mineral Appearance & ColorMineral Appearance & Color

• Two obvious clues used to identify minerals

• These clues are not enough to correctly identify a mineral

Mineral Appearance & ColorMineral Appearance & Color

• For example – Which one of the following is gold?

Mineral Appearance & ColorMineral Appearance & Color• The one on the left is gold and the one on the right is

pyrite (also known as fool’s gold).• Because they both look like gold, you cannot go just go

by appearance and color to identify the mineral.• Other tests need to be performed

Gold Pyrite (fool’s gold)

HardnessHardness

• A measure of how easily a mineral can be scratched

• Talc is so soft it can be scratched with your fingernail.

• Diamonds are the hardest substance on Earth and can only be scratched by other diamonds.

• So how do we tell how hard a mineral is?

• Moh’s Hardness Scale (pg. 37)– A scale developed by Austrian scientist

Friedrich Mohs that lists a list of common minerals and their hardness.

• Let’s say you have a clear, whitish material that you know is either fluorite or quartz…but your not sure because they have the same appearance and color.

• You try to scratch it with your fingernail but it doesn’t scratch. So you know that whatever it is, it has a hardness greater than 1.

 

• You then try to scratch it with the iron nail and you are able to scratch the surface. So you can conclude that the hardness of the clear, whitish material has to be greater than 2.5 but lower than 4.5.

• You can determine that the hardness of the unknown material is between 3 and 4. Well you already know that quartz has a hardness of 7 so the mystery material has to be fluorite.

 

Fluorite Quartz

Let’s Take Some Notes!!

• Appearance & Color– These clues are NOT enough to correctly

identify a mineral

•  Hardness– A measure of how easily a mineral can be

scratched

LusterLuster • The way a mineral reflects light.

• Either metallicmetallic or nonmetallicnonmetallic

• If it’s shiny like metal – it’s metallic

Hematite Graphite Pyrite

• If it’s dull, glassy, pearly, or silky - it’s nonmetallic

Talc(Silky)

Biotite(Pearly)

Obsidian(Glassy)

Let’s Take Some Notes!!

• Luster– The way a mineral reflects light (can be

metallic or nonmetallic)

Specific GravitySpecific Gravity• The specific gravity of a mineral is the ratio of

its weight comparedcompared with the weight of an equal volume of water (very similar to density).

• Gold has specific gravity of 1919

• It means gold is 19 times heavier19 times heavier than water.

19 times heavier

Specific gravitySpecific gravity

Let’s Take Some Notes!!

• Specific Gravity– The ratio of the minerals weight compared to

the weight of an equal volume of water (similar to density)

StreakStreak

• When a mineral is rubbed across a piece of porcelain tile (called a streak plate). A streak of powdered mineral is left behind.

• The streak test only works for materials that are softer then the plate. The streak plate has a hardness of 7 so you can only test minerals that have a hardness below 7.

• Gold and pyrite can be determined using a streak plate. Gold leaves a yellow streak and pyrite leaves a greenish black or brownish black streak.

• Some minerals may appear as one color but leave a completely different color streak.

• Some minerals will leave a streak on paper…like the graphite in your pencil

Let’s Take Some Notes!!

• Streak– The color of the mineral when in powdered

form (streak plate)

CleavageCleavage• Cleavage is the way that mineral breaks.• Minerals that break along smooth, flat surfaces

have cleavage.• The way the atoms are arranged make for a

smooth, clean break.• Mica has cleavage

FractureFracture

• Mineral that breaks uneven, rough, or jagged surfaces have fracture.

• Quartz has fracture

• If you were to take a layered cake and separate its layers, we would say that the cake has cleavage. But if we were to take our hand and jab it into the cake and pull it out, we would say that the cake has fracture.

CLEAVAGECLEAVAGE FRACTUREFRACTURE

Let’s Take Some Notes!!

• Cleavage & Fracture– Cleavage – minerals that break along smooth

flat surfaces– Fracture – minerals that break unevenly &

jagged

Other PropertiesOther Properties• Some minerals are magnetic, such as

magnetite, which is attracted to magnets.

• In calcite – light forms two separate rays as it passes through causing you to see a double image.

• Calcite will also fizz if you put some drops of hydrochloric acid on it.

Let’s Watch a Video!Let’s Watch a Video!