Rocks & Minerals
What exactly is a rock?
A rock is not a pure substance. It is a mixture of minerals. Minerals are
solid, crystalline (their atoms are arranged in regular, geometric patterns) and
non-living. Most of the minerals we find come from the first layer of the Earth,
called the crust. Minerals are made from one or more elements that have been
chemically combined into a compound.
Each mineral has a slightly different chemical recipe. For example gold is
made of just gold atoms. Diamonds are made of carbon atoms. Other minerals
are made of more than one element. For example, rubies have bits of aluminum,
oxygen, and chromium.
Idea: Think of a COOKIE to understand rocks. Your favorite cookie has several
ingredients depending on the type of cookie you’re making. ROCKS are the same.
Rocks are made of different minerals.
1. What are the ingredients? Every good cookie starts with a recipe. you
might need butter, sugar, eggs, flour, and chocolate chips. Rocks have
ingredients too, but instead of adding chocolate or butterscotch chips
you would add minerals… lots of different combinations and kinds.
2. What’s the recipe? What would happen if you added more of an
ingredient to your favorite cookie recipe? You’d end up with a different
tasting cookie. Rocks are the same. Depending on the different
quantity (or number) of minerals in each rock, you will have a different
kind of rock.
3. How are you baking them? One last thing to consider. If you burn your
cookies or take them out of the oven too early, you will end up with a
very different cookie than the one baked at the perfect time and
temperature. Rocks are the same! Depending on the way in which the
rock is formed – in hot volcanoes, deep in the Earth’s crust, pounded by
the ocean’s – you will end up with a different rock every time.
How many minerals does it take to make a rock? There are more
than 3,000 known minerals on Earth and all rocks are made up of
combinations of minerals, volcanic gas, older rock fragments, fossils, or
plant matter. Combinations of these minerals are what makes rocks
reddish in color (lots of iron) or milky white (lots of quartz) or sparkly
(lots of mica).
Some minerals are incredibly valuable because they are rare and
useful. Platinum, gold, and silver are used to make electronic devices.
These metallic elements are difficult to find – and can be expensive as a
result. Other minerals such as diamonds, rubies, and emeralds don’t
look like much until they are cut and polished. Not all minerals are
rare. Take talc for example. It’s used to make baby powder. Mica is
ground up to make eyeshadow. The value of a mineral depends on
how much of it there is in the world and how hard it is to get.
Vocabulary
1. mineral… A natural, solid material with particles arranged in a
repeating pattern.
2. streak… The color of the powder left behind when you rub a
material against a white tile called a streak plate.
3. luster… The way the surface of a mineral reflects light.
4. hardness…A mineral’s ability to resist being scratched.
Minerals
Almost all minerals are made from material that was never alive. True minerals
form only in nature. They are not made in a laboratory.
Forming of minerals:
1) Some mineral’s form in Earth’s mantle as high heat and pressure change
carbon into hard, sparkling crystals called diamonds.
Uses for diamonds: jewelry, used on cutting tools like drills and saws.
2) Some minerals, like calcite, form at or near Earth’s surface. Some calcite
forms in the ocean when calcium, oxygen, and carbon combine in sea
water. Calcite also forms when water evaporates in limestone caves.
Uses of Minerals
Some minerals can be used in nearly the same form they have in
nature. They don’t need much changing, refining, or processing to remove
other materials. For example… Silver and Copper can be used to make
musical instruments, electric wire, and jewelry. Gypsum can be used to
make plaster and wallboard. Graphite can be used in pencils. Halite, or
table salt, can be used to flavor and preserve food.
Some minerals can’t be used in their natural form. They must be
refined or changed to be useful. The mineral cuprite is made of copper and
oxygen. After cuprite is refined or changed, the copper can be used in
making pennies, pots & pans, and water pipes.
Mineral Properties (Ways to Identify)
A) Streak is the color of the powder left behind when you rub a material
against a white tile called a streak plate. Usually the streak is the same
color as the mineral.
B) Luster describes the way the surface of a mineral reflects light. Some
minerals look shiny, like aluminum foil looks. These minerals have a
metallic luster. Others look dull or dark. These minerals have a
nonmetallic luster. The sparkling appearance of a diamond is known as
a brilliant luster.
C) Hardness is a mineral’s ability to resist being scratched. Moh’s hardness
scale lists mineral’s that have a hardness from 1 to 10. A mineral with a
high number on the scale can scratch a mineral with a low number on
the scale.
Moh’s Hardness Scale
Level of Hardness
1
2
2.5
3
4
5
5.5
6
7
8
9
10
Mineral or Object
Talc
Gypsum
FINGERNAIL
Calcite
COPPER PENNY
Fluorite
Apatite
KNIFE
Orthoclasse
GLASS
Quartz
Topaz
Corundum
Diamond