Download 1 • Welcome to the GIA Junior Gemologist Program

• Welcome to the GIA Junior Gemologist Program™ Boy Scouts of
America Merit Badge Series for Geology
• The material in this presentation will help Boy Scouts work
toward their Geology merit badge, however there are a few
items such as topographic and geologic maps, that they will
have to research on their own.
• Please use the notes section to help you with additional
information for each slide.
• There are also optional activities that can be done with the list
of suggested materials.
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Geology is the science and study of the earth. Geology helps gem prospectors
decide where to look for new gem sources. They know that certain gem
deposits are associated with certain types of rock. This helps them narrow down
the search for gems.
L: Colombian emerald mine. R: Ice road trucks near Canadian diamond mine.
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• All rocks are made of minerals.
• Some rocks form at or near the earth’s surface and yet others form deep in
the earth’s crust or in the upper middle layer of the earth in the mantle.
• There are many kinds of rocks, but they all can be classified into three groups
based on how they formed:
Example
• Think about rocks like cookies. Cookies are made with more than one
ingredient like rocks.
• Some of those ingredients you can see for example, nuts, chocolate chips,
and oatmeal.
• Some ingredients you can’t see like eggs, sugar, salt, and baking powder.
• Rocks are made of many minerals, some you can see and some you cannot,
just like cookies.
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• Igneous rock is formed by the cooling and crystallization of molten rock
• The term igneous is derived from the Latin word for “fire”
• Scientists have divided igneous rocks into two broad categories based on
where the molten rock solidified (hardened)
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• Intrusive Igneous – also called Plutonic are those that solidified or
hardened below ground.
• Intrusive igneous rocks are formed when underground, melted rock
called magma, is trapped deep within the earth
• Some magma may feed volcanoes on the Earth's surface, but most
remains trapped below, where it cools very slowly over thousands or
millions of years until it solidifies (hardens)
• When magma cools and hardens slowly, the individual minerals in it
form large grains (or crystals) that are easy to see.
• Extrusive Igneous – also called Volcanic include all rocks resulting from
eruptions of lava.
• Extrusive, or volcanic, igneous rock is produced when magma exits
and cools outside of, or very near the Earth's surface
• These are the rocks that form from erupting volcanoes and from
cracks that ooze lava.
• Magma, called lava when molten rock erupts on the surface, cools and
solidifies almost instantly when it is exposed to the relatively cool
temperature of the atmosphere.
• Quick cooling means that mineral crystals don't have much time to grow, so
these rocks have a very fine-grained or even glassy texture.
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(picture 1)
Granite formed below the earth’s surface and had time to cool slowly and form
larger mineral crystals.
• You can see where the granite intruded into the pre-existing rock.
• The dark rock was already there and the lighter rock intruded into it.
• Can you see where pieces have broken away?
(picture 2)
In the next picture can you see a lava flow. Lava cools very quickly so you can
see lots of bubble-like cavities where gas was trapped.
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• Sedimentary rocks are formed by layers of sediments squeezed and pressed
together over a long period of time.
• Notice the different colors of layers in this large sandstone rock located in
Colorado Springs.
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• Metamorphic rocks can form from any type of rock including other
metamorphic rock
• This is an example of mountain building in action
• Can you believe that this was at one time flat? Nature deposits everything
horizontally
• Changes in the earth have caused this mountain to be squeezed, making the
mountain look wavy
• This mountain is a combination of limestone and slate
Example
• Let’s look at something we all know about…recycling. Plastic soda bottles
are melted and pulled to produce fiber filling for pillows, quilts and jackets
• This is similar to what happens to rocks during the metamorphic process.
They are completely changed
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• Here is a picture of the Himalayas todays. Notice how sharp and jagged the
surface terrain is.
• Spinel is a gemstone that can form in marble.
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Rocks can change. Nature deposits everything horizontally with gravity but
notice how the folded rock looks like a sideways “s” because compressional
forces underground smashed the mountains together.
 Optional activity if you have different rock examples for student to
identify
Igneous: pumice, granite, lava, obsidian
Sedimentary: sandstone, limestone
Metamorphic: slate, marble
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Geologists are key to understanding where to build homes safely, drill for oil and
look for gemstones.
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Here are some advanced careers in geology:
• Paleontology is the scientific study of prehistoric life, which can be found in
fossils buried in the rocks.
• Mineralogy is a subject of geology specializing in the scientific study of
chemistry, crystal structure, and physical (including optical) properties of
minerals and the processes that create them.
• Volcanology (also spelled vulcanology) is the study of volcanoes, lava,
magma, and related geological, geophysical and geochemical phenomena.
• Hydrology is the study of the movement, distribution, and quality of water on
Earth and other planets, including water resources and environmental
watershed sustainability.
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• Mineralogy is the science that involves the chemistry, crystal structure, and
physical (including optical) properties of minerals and the processes that
create them.
• The pink mineral is morganite. The other image shows talc.
Example
• Think about minerals like the ingredients in cookies. Mineral crystals in rocks
are like the large ingredients you can see in a cookie: chocolate chips,
oatmeal, M&M’s, etc.
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An object has to have these five features to be classified as a mineral: solid,
inorganic, formed in nature, specific chemical composition and a crystal
structure.
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Click middle of slide with mouse to start animation
• Repeating atomic structure
• Nature’s building blocks
Example
• When building a brick wall, you would want to make sure that all the blocks are close
to the same size and line up evenly when stacked.
• You also need mortar to hold the bricks together right.
• The bricks are like atoms in a crystal, and the mortar is the bond that holds them
together.
• If the blocks that made up your wall weren’t lined up perfectly would your wall still be
strong and stable?
• Probably not. It would have weak points where the bricks weren’t stacked correctly.
• This is also true for mineral crystals.
• This shows the atomic structure for sapphire and the crystal it will produce.
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The most exciting aspect of minerals are their beautiful and elegant crystal
forms
• A mineral’s crystal form is an exterior expression of the mineral’s internal
atomic structure. A mineral’s shape is determined by the pattern that the
atoms follow.
• This is emerald
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Mohs Scale of Hardness
Hardness –
• Hardness refers to a mineral’s resistance to being scratched
• The system for measuring a mineral’s hardness was developed by a German professor
and mineralogist by the name of Dr. Frederich Mohs
• The Mohs Hardness Scale and ranges from 1 – 10
• 1 is the softest mineral, for example talc
• Talc can be scratched using your fingernail
• 10 which is on the other end of the scale and is the hardest mineral
• Diamond is 10 and can scratch everything below it. Now don’t be fooled, when
they say only diamond can scratch glass.
• That is not true, any material that has a hardness greater than glass (5-6 on the
Mohs scale) can scratch glass.
Example
• Glass-like plate at grocery store is synthetic corundum (9)
• Emery board to file nails can be made with diamond (10), corundum (9), or garnet (7)
• Very high-end watch faces made with synthetic sapphire (Rolex, Bulgari)
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Although visible light looks white, it’s actually a combination of the spectral
colors: red, orange, yellow, green, blue, and violet. Each color represents
lightwaves of different energies. And white light is the sum of all these waves
traveling together in the same direction.
When light shines on a stone, some of the colors get absorbed. The light you
see – the color of the stone – represents the light that was returned to your eye
without being absorbed (selective absorption). It’ influenced mostly by the
stone’s chemical composition and crystal structure.
 Optional activity if you have different colored minerals
Example: amethyst (purple), citrine (orange) and rock crystal (colorless)
are all quartz
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The “streak” of a mineral is the color of the powder residue left behind when it is
scratched across an unglazed ceramic tile. This test is useful when
distinguishing opaque and colored materials. Hematite, which is metallic black in
color, leaves a red streak while galena, which can look similar to hematite,
leaves a gray streak.
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Luster is the way light interacts with the surface of a mineral. There are several
categories of luster:
• Adamantine minerals possess a superlative luster, which is most notably
seen in diamond.
• Subadamantine minerals have a lesser (but still relatively high) degree of
luster, like garnet or cubic zirconia.
• Dull minerals exhibit little to no luster, due to coarse granulations which
scatter light in all directions, like talc.
• Greasy minerals resemble fat or grease, like some kind of opals.
• Metallic minerals have the luster of polished metal, and with ideal surfaces
will work as a reflective surface, like pyrite or hematite.
• Pearly minerals consist of thin transparent co-planar sheets. Light reflecting
from these layers give them a luster reminiscent of pearls, like muscovite.
• Resinous minerals have the appearance of resin or smooth surfaced plastic,
like amber.
• Silky minerals have a parallel arrangement of extremely fine fibers, giving
them a luster reminiscent of silk, like selenite.
• Submetallic minerals have similar luster to metal, but are duller and less
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reflective, like cinnabar.
• Vitreous minerals have the luster of glass, like calcite, quartz and fluorite.
• Waxy minerals have a luster resembling wax, like jade or lapis lazuli.
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Gemology is the science, art and profession of identifying and evaluating
gemstones. It may be considered a branch of mineralogy.
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• Rough and faceted diamond
• Beauty
• Being able to bring out the beauty in a gemstone.
• An attractive gemstone can come from an unattractive rough (uncut
material).
• Rarity
• Not common or hard to find
• What makes these diamonds very rare is that diamonds are normally
colorless, meaning they don’t have any color. These are colored, blue,
yellow, green and pink, making them even more rare.
• Durability
• Won’t break easy
• Holds up to everyday wear in jewelry
• Resistant to abrasion, fracturing and chemical reactions
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Group – The garnet group, a family of closely related mineral species.
Species - Andradite, one of several important species of gem garnets.
Variety – Demantoid, the green variety of the species andradite.
The garnet group is a family of gems with the same crystal structure and the
same basic chemistry of aluminum, silicon, and oxygen. Their differences lie in
the other chemical elements they contain, which give them differing colors and
properties.
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• Inclusions can be a variety of objects enclosed within a polished gemstone or
those that extend into it from the surface.
• They can be other minerals, gas or liquid.
• Lily-pad inclusions in peridot are caused by stress fractures usually
surrounding a small crystal. This is characteristic of peridot.
• Emeralds can have a three-phase inclusion – a mineral crystal, next to a gas
bubble, all enclosed in liquid.
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Inclusions cause special effects in some gemstones.
• These stones are called phenomenal stones, and they do tricks!
• They can change color in different lighting or reveal special effects
• They are light reactive so you need a good light source to see them.
• Left: moonstone, middle: opal, right: cat’s eye chrysoberyl with diamonds
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Here are some careers in gemology.
• You could work in a retail jewelry store and work your way up to managing it.
• You could be a wholesale colored stone buyer, flying to exotic locations like
Thailand and Sri Lanka to purchase large quantities of stones.
• You could be a jewelry designer, using both traditional hand designs and new
technologies with CAD/CAM, computer aided design/computer aided
manufacturing.
• Or you could work in a laboratory using microscopes and other equipment to
grade diamonds or identify colored stones.
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Uses for igneous rock:
• Native Americans carved arrowheads from obsidian.
• Granite is used for both headstones at the cemetery and counter tops in the
kitchen because of its long lasting durability.
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Uses for sedimentary rock:
• Brownstone is used in architecture for buildings.
• Coal is also sedimentary, formed by layers of organic material. It’s used in
power plants.
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Uses for metamorphic rock:
• Slate is used for rooftop tiles or in thin layers, it was once used for chalk
boards in schools.
• Marble is a very durable rock that has been used for centuries in sculptures
and architecture.
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Uses for minerals:
• Scanner plate at grocery store is coated in manmade corundum, 9 on Mohs
Hardness scale.
• Diamond dust is used on spinning wheels to facet diamonds or on saw blade
tips to make them harder, 10 on Mohs Hardness scale.
• Tiny garnet crystals can cover nail files, 6.5 – 7.5 on Mohs Hardness scale,
fingernail is 2.5
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Uses for minerals:
• Beryl is used for nuclear power as well as fluorescent lights.
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