Rocks and Minerals
ID Lab
Juniata College
Science in Motion
Middle School
Rocks and Minerals
ID Lab
Introduction:
Rocks and minerals have many uses in our everyday lives. For everything from using
diamonds in electronics and industry to various minerals that are used as vitamins
minerals. We could not live in this industrial and technology age with out minerals of all
types. Can you think of any uses for rocks or minerals?
Minerals are identified my several techniques or characteristics of the minerals. These
characteristics include cleavage, fracture, luster, color, streak color, hardness, density,
and reactivity with an acid.
Purpose/Objectives:
Students will recognize the differences between igneous, metamorphic, or sedimentary
rocks
Students will identify 10-14 or more rocks using chemical and physical means
Students will answer questions about the rocks, rock cycle, and type of rock and rock
characteristics.
Equipment/Materials:
o Teacher rocks (labeled)
o Students unknown rocks, the same as the teacher rocks (7)
o ID kits(7) for identifying rocks by characteristics (glass, steel nail, bottle for HCL,
streak plate, copper strip, magnet, beaker for water) such as streak, hardness,
cleavage, magnetic properties, density
o Ice cube trays (7) for organizing rocks and minerals
o Instruction sheet, key and worksheets.
o Books
Peterson’s Field Guide to Rocks
Rocks and Minerals of PA
Various maps are available that would show the location of types of rocks and
minerals in PA. (upon request)
Safety:
o Students should not attempt to break or fracture the rocks. This will damage the
rock samples and could result in potential eye injury. Safety glasses must be
worn by everyone, if a rock hammer is being used.
o Caution should be used when dealing with any sharp objects, such as glass,
copper plate, or the steel nail.
o If hydrochloric acid is used, safety glasses must be worn and all times and all acid
safety precautions must be taken in the case of spills. Avoid contact with skin.
o In the case of broken glass, notify your teacher and then she will clean up the
glass with a dust pan.
Procedure:
1.
2.
3.
4.
5.
6.
Obtain a sample set of rocks for identification.
Obtain the rock and mineral identification manuals.
Obtain the rock and mineral identification kit.
Read the directions on the “identifying Rocks and Minerals” lab.
Answer the questions on the first page of the lab.
Observe and note the color of your rock or mineral. (Keep in mind that physical
color is the least valuable test for identification.)
7. Perform the following physical and chemical tests to each rock in the unknown
rock samples.
a. Close Examination of the rock
i. Color: Observe and record the color of the rock or mineral.
Obvious, but not always definitive. Sulfur is (almost) always
yellow, and there are a few others, but not many minerals have a
fixed color. Small amounts of impurities can drastically change a
mineral's color.
ii. Luster: The quantity and quality of light reflected from the
surface. Most identification schemes begin with a simple
classification based on luster. Because of this, luster is the first
fundamental test to be made when identifying any mineral. Most
are relatively obvious, but some minerals can exhibit a range of
lusters (ex. Hematite).
1. Metallic: looks like a metal. Metallic minerals are
commonly shiny and opaque
2. Non-metallic: doesn't look like a metal. There are many
subtle differences in the non-metallic lusters, but most are
relatively dull, and are often transparent to translucent on
thin edges.
3. Waxy
4. Vitreous or glassy
iii. Observe the grain size and texture distribution (uniformity)
Cleavage: How a mineral breaks is determined by its internal structure,
and is there very important. Unfortunately, it can also be the hardest to
determine (sorry). There are two (2) major subdivisions: fracture and
cleavage.
i. DO NOT BREAK YOUR ROCKS!!!!!!!!
ii. Fracture: The mineral just breaks, leaving an uneven surface. Most
are irregular but there are some special cases (ex: the conchoidal
fractures common to quartz and glass)
iii. Cleavage: The mineral splits along closely spaces parallel planes,
leaving a mirror surface which will flash at you if rotated in the
light. Cleavage is controlled by the internal crystalline order of the
mineral. A mineral can have 1, 2, 3, 4, or 6 planes of cleavage. If
more than one (1) plane is present, it is important to note the angles
between the cleavages. Cleavage can be obscured, but is definitive
when present. Terms such as Perfect, Good in 2 directions, Poor,
etc. are used to indicate the quality or strength of the cleavage.
Cleavage can be tough to distinguish from external crystalline
form, and it's always a shame to break a good "crystal" when
checking for cleavage.
c. Specific Gravity:
i. Defined as "the weight of a specific volume of a mineral divided
by the weight of an equal volume of water (at 4°C.)" Since water is
always 1.0, it's the same number as density without any units (they
cancel). This is almost impossible to measure in the field, but a
rough approximation and be determined.
ii. Hit: Some igneous rocks will be less dense than water and float,
such as pumice.
d. Effervescence/ Acid Test
i. Drop a drop or two of hydrochloric acid or lemon juice (acetic
acid) on the rock
ii. Does it fizz?
iii. This would mean that carbon dioxide is being given off and the
rock is a carbonate (limestone)
iv. Minerals containing calcium carbonate (CaCO3) will generally
react when exposed to hydrochloric acid (HCl). Carbon dioxide
(CO2) is released and the mineral or rock literally "fizzes." Some
may need to be powdered (increases surface area) before any
reaction can take place
e. Hardness: Test the Mohs Hardness of the rock/mineral
i. Hardness is the resistance of a mineral to scratching. It does NOT
refer to how easily the mineral is broken. Hardness is a measure of
the bond strength between atoms. If these bonds are strong, the
mineral is not easily scratched. Minerals with weaker bonds are
more easily scratched. Pencil "lead" is softer than paper, so it
b.
f.
g.
h.
i.
writes. Try writing with a steel-tipped pencil. Now the pencil rips
the paper. This is clearly related to the relative hardness of each
substance. Hardness in minerals can vary due to impurities, but is
usually definitive. We determine the relative hardness of minerals
using a scale devised by mineralogist Friedrich Mohs. The scale
assigns hardness to ten common index minerals, and is based on
the ability of one mineral to scratch another.
ii. Try to scratch the various substances (see key) with the rock
iii. Try to scratch the rock with the various substances
Streak test:
i. Rub the rock on the white unglazed porcelain tile.
ii. The color of the powdered mineral. Streak can be definitive. Good
examples include hematite (always a deep red no matter what form
it's in) and chromite (distinguished from the hundreds of other
black minerals by its chocolate-brown streak).
iii. Observe and record the color of the streak on the tile.
Magnetism: Some rocks have natural magnetism. Magnetite, i.e., the lode
stone, is naturally magnetic
Taste: Some minerals have a distinctive taste. Notable examples
include Halite (rock salt), and Chalcanthite (a copper arsenide - be
careful with this one!!). DO NOT TASTE THESE ROCKS!!!
Smell: Some minerals have a distinctive odor. Sulphur is a good
example. Remember to waft all chemicals, including rocks in the
laboratory.
7. Record all results on the chart of rock characteristics.
Mineral & Rock ID
The following rocks in the small baggie. They are rocks that might be a
little easier for middle school students to ID and there are sedimentary,
igneous and metamorphic rocks in the baggie.
I would suggest using 10-14 of these rocks for your Rock ID Lab. You
can use any rocks you wish with your classroom, put please notify us if
the same rocks are not in the small baggie.
You can fill in the following chart similar to the ice-cube tray before you
start as a key for yourself. You can also give a blank sheet to the
students for their answers. You can give them a word bank consisting
of only the rocks you give them, or add a few more rock names or no
work bank at all.
You will need to check the organization of the rocks in the ice cube tray
routinely because they often get switched around.
Thanks
1. Talc
2. Galena
3. Pyrite
4. Halite
5. Graphite
6. Slate
7. Pumice
8. Mica, Muscovite
9. Schist, Mica
10. Conglomerate
11. Granite
12. Gypsum
13. Quartz
14. Sandstone
15. Limestone
16. Magnetite
17. Obsidian
18. Garnet
19. Calcite
20.Pumice
Mineral & Rock ID
1
2
3
4
5
6
7
8
9
10
11
12
13
14
The Mohs Scale of Relative Mineral Hardness
The Mohs scale was devised by Friedrich Mohs in 1812 and has been a valuable aid
to identifying minerals ever since. Here are the ten standard minerals in the scale.
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Feldspar
7. Quartz
8. Topaz
9. Corundum
10. Diamond
You use the scale by testing your unknown mineral against one of these standard
minerals. Whichever one scratches the other is harder, and if both scratch each
other they are both the same hardness.
The Mohs scale is strictly a relative scale, but that's all that anyone needs. In terms
of absolute hardness, diamond (hardness 10) actually is 4 times harder than
corundum (hardness 9) and 6 times harder than topaz (hardness 8). Because it isn't
made for that kind of precision, the Mohs scale uses half-numbers for in-between
hardnesses. Dolomite, which scratches calcite but not fluorite, has a Mohs hardness
of 3½ or 3.5.
There are a few handy objects that also fit in this scale. A fingernail is 2½, a penny is
3, a knife blade is 5½, glass is 5½, and a steel file is 6½.
The following is a range of the useful scale of common materials for the Mohs
Hardness Scale:
1.0-2.5 Won’t scratch a fingernail
2.5-3.5 Scratches fingernail, but wont scratch copper
3.5-5.5 Scratches copper, but won’t scratch glass.
5.5-6.5 Scratches glass, but won’t scratch steel.
6.5+ Scratches steel
Mohs hardness is just one aspect of identifying minerals. Along with hardness, you
need to consider luster, cleavage, crystalline form, color, and rock type to zero in on
an exact identification.
Rock
Number
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Color &
Luster
Streak
Color
Hardness
Cleavage
Yes or No
O
of angle
Specific
Gravity
> or <
water
Acid Test
Fizz
Yes or No
Extra Tests
Smell
Magnetism
Rock
Sedimentary If
Number Igneous or
sedimentary
Metamorphic Clastic,
Chemical or
Organic
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
If Igneous
IntrusivePleutonic or
ExtrusiveVolcanic
If
Igneous
Felsic or
Mafic
If
Name of
Metamorphic Rock
Foliated or
Non Foliated
Vocabulary:
Rock Cycle: the process by which rocks are formed, altered,
destroyed, and reformed by geological processes and which
is recurrent, returning to a starting point. The rock cycle is
made of the following types of rocks, each of which can
change into the other: igneous rocks, metamorphic rocks,
and sedimentary rocks.
Igneous rocks
http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html
Igneous rocks (from the Greek word for fire) form from when hot, molten rock (magma)
crystallizes and solidifies. The melt originates deep within the Earth near active plate
boundaries or hot spots, and then rises toward the surface. Igneous rocks are divided into
two groups, intrusive or extrusive, depending upon where the molten rock solidifies.
Extrusive igneous rock
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 at erupting volcanoes and
oozing fissures. The 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. Hot gas bubbles are often trapped in the
quenched lava, forming a bubbly, vesicular texture. Pumice, obsidian, and basalt are all
extrusive igneous rocks.
The cinder cone above and the close up at right are made of basalt.
Intrusive igneous rock
Intrusive, or plutonic igneous rock forms when magma is trapped deep inside the Earth.
Great globs of molten rock rise toward the surface. Some of the magma may feed
volcanoes on the Earth’s surface, but most remains trapped below, where it cools very
slowly over many thousands or millions of years until it solidifies. Slow cooling means
the individual mineral grains have a very long time to grow, so they grow to a relatively
large size. Intrusive rocks have a coarse grained texture. The image at right shows
granite, an intrusive igneous rock.
Samples of Igneous rock
Volcanic rock
Igneous rock that cools and solidifies at or very near the Earth’s surface. Volcanoes
produce volcanic rock.
Granite
A coarse-grained intrusive igneous rock with at least 65% silica. Quartz, plagioclase
feldspar and potassium feldspar make up most of the rock and give it a fairly light color.
Granite has more potassium feldspar than plagioclase feldspar. Usually with biotite, but
also may have hornblende.
Lava
Magma that reaches the Earth’s surface through a volcanic eruption. When cooled and
solidified, forms extrusive (volcanic) igneous rock.
Pegmatite
A very coarse-grained igneous rock, commonly with a granitic composition. Usually
forms from molten rock rich in water or other volatiles that facilitate the growth of large
crystals. Forms sills and dikes.
Sedimentary Rocks
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living
organisms. They form from deposits that accumulate on the Earth’s surface. Sedimentary
rocks often have distinctive layering or bedding. Many of the picturesque views of the
desert southwest show mesas and arches made of layered sedimentary rock.
Clastic sedimentary rock
Clastic sedimentary rocks are the group of rocks most people think of when they think of
sedimentary rocks. Clastic sedimentary rocks are made up of pieces (clasts) of preexisting rocks. Pieces of rock are loosened by weathering, and then transported to some
basin or depression where sediment is trapped. If the sediment is buried deeply, it
becomes compacted and cemented, forming sedimentary rock.
Clastic sedimentary rocks may have particles ranging in size from microscopic clay to
huge boulders. Their names are based on their clast or grain size. The smallest grains are
called clay, then silt, then sand. Grains larger that 2 millimeters are called pebbles. Shale
is a rock made mostly of clay, siltstone is made up of silt-sized grains, sandstone is made
of sand-sized clasts, and conglomerate is made of pebbles surrounded by a matrix of sand
or mud.
Biologic sedimentary rock
Biologic sedimentary rocks form when large numbers of living things die, pile up, and
are compressed and cemented to form rock. Accumulated carbon-rich plant material may
form coal. Deposits made mostly of animal shells may form limestone, coquina, or chert.
Chemical sedimentary rock
Chemical sedimentary rocks are formed by chemical precipitation. The stalactites and
stalagmites you see in caves form this way, so does the rock salt that table salt comes
from. This process begins when water traveling through rock dissolves some of the
minerals, carrying them away from their source. Eventually these minerals can be
redeposited, or precipitated, when the water evaporates away or when the water becomes
over- saturated with minerals.
Samples of sedimentary rock
Sandstone
Sedimentary rock made mostly of sand-sized grains.
Shale
Sedimentary rock derived from mud. Commonly finely laminated (bedded). Particles in
shale are commonly clay minerals mixed with tiny grains of quartz eroded from preexisting rocks. Shaley means like a shale or having some shale component, as in shaley
sandstone.
Bedding
Sedimentary layers in a rock. The beds are distinguished from each other by grain size
and composition, such as in shale and sandstone. Subtle changes, such as beds richer in
iron-oxide, help distinguish bedding. Most beds are deposited essentially horizontally.
Chert
A very fine-grained sedimentary rock made of quartz. Usually made of millions of
globular siliceous skeletons of tiny marine plankton called radiolarians. Black chert is
called flint.
Metamorphic Rocks
Metamorphic rocks started out as some other type of rock, but have been
substantially changed from their original igneous, sedimentary, or earlier
metamorphic form. Metamorphic rocks form when rocks are subjected to high heat,
high pressure, hot, mineral-rich fluids or, more commonly, some combination of
these factors. Conditions like these are found deep within the Earth or where tectonic
plates meet.
In metamorphic rocks some or all of the minerals in the original rock are replaced,
atom by atom, to form new minerals.
It’s not hard to see that this metamorphic rock, called gneiss, has been intensely
folded! This rock had to have been under very high pressure and temperature to
allow it to fold like this without breaking. Photo by Edward P. Klimasauskas, USGS.
Metamorphic rocks are often squished, smeared out, and folded. Despite these
uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they
would become igneous rocks!
Foliated metamorphic rock
Foliation forms when pressure squeezes the flat or elongate minerals within a rock so
they become aligned. These rocks develop a platy or sheet-like structure that reflects
the direction that pressure was applied in. Slate, schist, and gneiss (pronounced
'nice') are all foliated metamorphic rocks.
Non-foliated metamorphic rock
Non-foliated metamorphic rocks do not have a platy or sheet-like structure. There
are several ways that non-foliated rocks can be produced. Some rocks, such as
limestone are made of minerals that are not flat or elongate. No matter how much
pressure you apply, the grains will not align! Another type of metamorphism, contact
metamorphism, occurs when hot igneous rock intrudes into some pre-existing rock.
The pre-existing rock is essentially baked by the heat, changing the mineral
structure of the rock without addition of pressure.
Samples of metamorphic rocks
Schist
Metamorphic rock usually derived from fine-grained sedimentary rock such as shale.
Individual minerals in schist have grown during metamorphism so that they are
easily visible to the naked eye. Schists are named for their mineral constituents. For
example, mica schist is conspicuously rich in mica such as biotite or muscovite.
Source - US Geological Survey Western Earth Surface Processes Team and the
National Park Service.
http://www.desertusa.com/geofacts/rocks_igne.html
Mineral - A mineral is a naturally occurring, inorganic, crytalline solid, that has a
definite chemical composition, and is stable over a range of temperatures and pressures.
Example - Quartz is a mineral, it is found in nature, it forms without the help of plants
and animals, it is crystalline, and it has a definite chemical composition (SiO2, two
oxygen atoms for every one silicon atom). It is stable, both at low and high temperatures,
but is unstable at very high temperatures ( > 600 C). It is stable at low to moderate
pressures and is unstable at high pressures (equivalent to burial many tens of kilometers
deep). Another common mineral is feldspar.
Rock - A rock is an aggregate (a combination) of one or more minerals. It may be
igneous, sedimentary or metamorphic.
Example - A mixture of crytals of quartz and feldspar is a rock called granite. Granite
may also have other minerals such as micas, pyroxene, and amphiboles in lesser amounts,
as well as many others in trace quantities.
Although there are over 4000 different minerals and hundreds of rock types, there are
only about 8 common minerals and 20 common rocks found at the Earth's surface. This
makes it relatively easy to learn how to recognize the vast majority of minerals & rocks
that you will ever see. All it takes is a little practice.
The most common minerals are: quartz, potassium feldspar, plagioclase feldspar, olivine,
pyroxene, amphibole, mica, and calcite.
The most common igneous rocks are: rhyolite, granite, andesite, diorite, basalt, gabbro,
peridotite, obsidian, pumice, and scoria.
The most common sedimentary rocks are: shale, sandstone, conglomerate, limestone,
and tillite.
The most common metamorphic rocks are: slate, phyllite, schist, gneiss, marble, and
quartzite.
http://www.casdn.neu.edu/~geology/department/staff/colgan/iceland/rocks.htm
Rocks and Minerals
Id Lab
Teacher Notes
PA Standards:
Science and Technology Standards
3.5 Earth Sciences: Describe earth features and processes
3.5.7 A
Describe the processes involved in the creation of geologic features
(rock cycle)
Explain how the rock cycle affected rock formation in the state of PA.
3.5.10A
Describe and identify major types of rocks and minerals
3.2 Inquiry and Design
3.2.7 B Apply process knowledge to make and interpret observations
Measure materials using a variety of scales
Design controlled experiments
Lab Time:
This laboratory assignment will usually take at least two days and up to four
days.
It can be broken into the different rock types such as igneous, sedimentary
and metamorphic of three separate labs of one or two days each.
Preparations:
Students should wear eye protection (safety glasses) when dealing with
chemicals.
Surfaces will become dirty and dusty when dealing with rocks. Table tops
should be cleaned routinely to avoid damage to clothing.
Considerations/Students should already know:
Students should be familiar with the rock cycle and the processes by which
rocks are formed.
Students should know the meaning of the vocabulary words.