What is a crystal?
How do minerals form?
What factors affect the size and shape
of crystals?
What are the different crystal shapes?
The 5 characteristics of a mineral
• Solid
•Natural (found in nature)
•Inorganic (never living)
• Orderly internal structure of atoms (crystal structure)
• Chemical composition (chemical formula)
Mineraloid - lacks an orderly internal structure
Unit 4
PHENOMENON:
What did you observe?
What evidence do you have?
Crystal Formation
OBJECTS:
.
What objects
are interacting?
copper wire and
silver nitrate
Salt solutions in
100% and 50%
concentrations
Salol cooling and
crystalizing
Granite rock crystals
Graphite and
diamonds
Crystal models and
crystals samples in
well plate
MOTION /STRUCTURE
Describe the structure that in the model that
explains your observations
Part A:
Making (silver) Crystals
http://www.youtube.com/watch?v=bJDeoah
-Cd0 snowflake crystals
Silver nitrate ‘crystals’
pic from phone
• Although not flat surfaces,
the silver
atoms arrange
in a regular repeating
pattern
Definition of
crystal
Part B: Concentration
and Crystal Formation
1. Ions (such as salt or calcium) are dissolved in water.
2. The water EVAPORATES, and the ions form minerals
such as halite, calcite, gypsum, limestone.
http://www.classzone.com/books/earth_science/terc/content/inve
stigations/es0506/es0506page09.cfm
Part C: Crystal and Space
http://www.youtube.com/watch?v=HeiMfLmJtzk
Mexico's Cueva de los Cristales
(Cave of Crystals) contains some of
the world's largest known natural
crystals—translucent beams of
gypsum as long as 36 feet (11 m).
Volcanic activity 26 million years
ago created Naica mountain and
filled it with high-temperature
anhydrite gypsum. When magma
underneath the mountain cooled
and the temperature dropped, the
gypsum that had been dissolved for
millions of years began to be
deposited in the caves in the form of
huge selenite gypsum crystals.
100% concentration
100% concentration
25% concentration
25% concentration
Draw Particle diagrams to show (model) how the
crystals formed out of a solution
Salt dissolved in water
100% concentration
Water
25% salt solution
salt
salt arranged into
crystals
White Board Session review
• WB is neat, organized, readable
• All members of the group are prepared to explain a
part of the WB
• All group members are prepared to answer
questions about the WB
• Address questions and answers to the entire class
• No judgment statements –ask good questions
• It’s okay to make mistakes –that’s how we learn
• Be respectful of the presenters.
• Every student is responsible for all the information
learned from the discussion
Factors that determine crystal size:
Concentration
Space
Time / rate
http://www.classzone.com/books/earth_scien
ce/terc/content/investigations/es0506/es0506
page01.cfm?chapter_no=05
ES0506
Outside
inside
Part E: Observe
crystals
Under a stereoscope, compare the size of
the crystals for 3 magma rocks
Granite
Basalt
Obsidian
The Magma Process:
(pg.97)
• Molten (liquid) rock in a magma
chamber
At, near or under earth’s surface, rises
• The magma begins to COOL.
The atoms, ions and molecules combine
to form various mineral compounds.
• The molecules arrange into an orderly repeating
pattern to form CRYSTALS.
http://www.youtube.com/watch?v=1I5Qc73o5Vk bismuth
quartz
Rate / Time
• The RATE at which the molten magma
cools determines the crystal size.
• Predict:
If the magma cools at a s-l-o-w-l-y
(under the surface taking hundreds of years)
then the crystals will be…
well-formed
granite
• If the magma cools quickly (weeks) the crystals
will be small / microscopic / not well-formed
(Look at basalt with a hand lens or scope)
• Predict:
• If the magma cools at a very fast rate, quickly,
then the crystals will…. None
example:
obsidian a volcanic rock, cools instantly.
so it has no crystal structure, but a
glass-like structure
Crystallization of Salol Lab
Slow cooling and
crystalizing
Quick cooling and
crystalizing
Part E:
Rate of Cooling and
Size of crystals in Granite
• Granite contains 3-4 main minerals.
quartz
________:
clear, whitish, transparent
Feldspar (potassium) pink, salmon-colored
_______________:
Hornblende (amphibole)
___________________:
black, gray, dull
Mica - biotite
________________: black, shiny
Each mineral melts / crystallizes at its own temperature between 1300ºC and 500ºC
500°C
Rank the order in which the
minerals in granite will crystallize.
Hornblende (amphibole)
• First to cool and crystallize ___________
Biotite mica
• 2nd to crystallize ___________________
Feldspar (potassium) - pink
• 3rd to crystallize ___________________
quartz
• Last to crystallize _________________
So. . . Quartz is the LAST to crystallize, so it is usually shapeless.
The kind of mineral that is formed
depends on…
1. Which elements are present when it forms
2. The amount of an each element present.
* The same magma chamber can form
different minerals.
Bellwork
1. What is the #1 most abundant element in
the Earth’s crust.
2. List the five characteristics of a mineral:
3. What is the hardest and softest mineral on the
Moh’s Scale of Hardness?
4. Define a crystal:
5. How does a fast rate of cooling affect the size of
crystals? Slow rate?
Factors that affect the size and
shape of crystals
 Concentration
 Space
 Time / rate
Temperature
Pressure
Where do
diamonds form?
The Pressure Process:
1. Rock or mineral is exposed to extremely high pressures
and temperatures, and the minerals begin to break down.
2. As pressure and temperature increase, the molecules
RE-FORM into new minerals!
http://www.classzone.com/books/earth_science/terc/content/investigations/es0506/es0506page09.cfm
At what
temperature and
depth does
graphite exist?
Temp:
Pressure:
At what
temperature and
pressure do
diamonds form?
Temp:
Pressure:
Compare the properties of a
diamond and graphite
Color
Luster
Hardness
Cleavage
Crystal structure
Graphite and diamonds are BOTH made of
just CARBON atoms
Make a particle diagram of the atoms
graphite
diamond
Synthetic, man-made diamonds
• It takes Gemesis Diamond Co. four days to grow a diamond of an
average size of 2.5 carats. The process begins by placing a
microscopic diamond grain into a 4,000-pound machine about the
size of a kitchen oven. Under hundreds of thousands of pounds of
pressure and at temperatures as high as 2,700 °F, the nugget
grows, one atom at a time.
• The Gemesis process mimics a diamond's development deep
underground. Apollo Diamond, based near Boston, takes a different
tack, imitating the way diamonds are made in space. Through
chemical vapor deposition, Apollo's process pumps gas into a
chamber that essentially rains carbon and forms a diamond nugget
from a "seed" within two to four weeks time.
• https://www.youtube.com/watch?v=48NoIICJ2CQ
Genisis diamonds
http://channel.nationalgeographic.com/channel/videos/
man-made-diamonds/
Synthetic Diamonds
Polymorphs.
Minerals which have the same chemical
make-up, but different crystal structures
Both diamond and graphite contain
only carbon atoms.
Part F:
Crystal Shapes
(page 99)
Crystal:
the orderly arrangement of
the ions, atoms and
molecules that determines
the shape of each
mineral’s crystals.
Salt crystals
Potassium nitrate crystals
http://www.classzone.com/books/eart
h_science/terc/content/investigations/
es0506/es0506page05.cfm
Part F:
Crystal Shape Activity
Paper
model
letter
Look at the
crystal samples
in the trays
under the
stereoscopes.
Match them to
the crystal
models.
Use table on
page 99 in
your text book
A
Crystal
name
Cubic
Example
Mineral
name
Halite
Tray
sample
1
(Salt)
C
Tetragonal
Zircon
2
F
Hexagonal
Emerald
3
Topaz
D
Orthorhombic
B
Monoclinic
4
Sulfur
Gypsum
5
Mica
E
triclinic
turquoise
6
Graphing in WB’s
Factors that affect
crystal growth:
• Concentration
• Space
• Time to cool or
Rate of cooling
• Temperature
• Pressure
Select TWO factors
and construct two
graphs that show the
relationship between
them and crystal size
and shape.
Example:
If….
Crystals had
enough
SPACE to
form
A lot of large,
well-formed
crystals
Few,
shapeless
crystals
Low
concentration of material
high