Connecticut Rocks

Teacher Sheet

For the first exercise, students should bring in their favorite rock that they found near their house they live in now.  If they don't have a favorite rock, they can find one somewhere near the school or their home.  Everyone needs to bring in a rock.

The Rocky Start exercise uses a variety of rocks from the three different rock groups igneous, sedimentary and metamorphic.  If the classroom doesn't already have a rock collection, rocks can be collected by you, purchased from a company like Wards, or purchased from the DEP store.  It would be best to use rocks you collect or the set sold by the DEP store so that all rocks are types found in Connecticut.  The students should be allowed to examine the rocks initially without previous experience at mineral or rock identification to let them develop their own observation skills.  The rocks need to be numbered.  A magic marker works well for numbering, as stick-on labels tend to fall off.  If the magic marker doesn't show up, paint white spots on the rocks first with acrylic paint.

Connecticut has four major types of igneous rocks.  Basalt, found in the Connecticut and Pomperaug Valleys, formed as liquid magma flowed out on the ground, cooling quickly into a fine-grained rock about 200 million years ago.  Coarse-grained pegmatite and granite formed from magmas that did not reach the surface, cooling very slowly over long time periods well below the surface.  Gabbro, also coarse-grained, has the same composition as basalt, is dark gray, but cooled slowly far below the ground surface.  The granite and pegmatite magmas were very high in silica, thus they have a different mineral composition and are light in color.  The gabbro and granite in Connecticut are actually partially metamorphosed, so technically they are now metagabbro and granitic gneiss.  The Cool Rocks exercise will give the students a chance to see how the size of crystals forming from a cooling melt is controlled by the speed of cooling.  Minor igneous rocks found in Connecticut include norite, diorite, porphyry, and syenite.

All Connecticut sedimentary rocks are found in the Connecticut and Pomperaug Valleys.  The most common is arkose, a type of sandstone that contains abundant feldspar.  Connecticut arkose was once extensively quarried for building stone, called brownstone.  Large brownstone quarry holes can be seen in Portland along the Connecticut River.  A small quarry now operates there to supply materials for restoration of old brownstone buildings.  The other sedimentary rock is a siltyshale, ranging in color from dark gray to reddish brown.

Most of Connecticut consists of metamorphic rocks, mainly schist and gneiss, although marble is found in western Connecticut and quartzite is found in various parts of the state.  Other metamorphic rocks include amphibolite, granofels, greenstone and mylonite.  In a few places schist is actually phyllite, although no areas are large enough to be mapped as such.

There are two excellent activities about metamorphic rock formation and the rock cycle in the following book,

Great explorations in Math and Science, 
Lawrence Hall of Science, 
University of California at Berkeley.

The two chapters covering these topics are,

"Formation of Metamorphic Rocks",  p. 75 - 80, 
"The changing Crust",  p. 85 - 92.

In the Connecticut Rocks Regroup exercise, students will organize the rocks they originally looked at into groups of igneous, sedimentary and metamorphic rocks.  You can then check their results.  If your classroom has enough samples, they can do this with more than one set of rocks.  This will help them discover that different samples of the same kind of rock do not look always look alike.  Descriptions and names you provide them after they group the rocks will help them learn what the different rock types look like.  They can then attempt to name their Favorite Rock, based on what they have learned from the previous exercises. 


5 x 7 inch index cards 
One set of 10 to 12 rock samples 
One hand lens or magnifying glass for each student 
Several triple beam balances or other instruments that measure mass 
Assorted graduated containers of various volumes and shapes for finding volume

For Cool Rocks 
2 votive candles with holders (small aluminum foil dishes) for each group of 4 students 
2 oz. Salol crystals 
Ice cubes (2 cubes per team, store in a cooler or a freezer) 
metal spoons (not plastic) for each group 
Quarter-teaspoon measuring spoon 
Paper towels 
2 paper or plastic cups (2 - 3 oz) per group 
2 lumps of modeling clay 
4 pairs of goggles

For Geologists with a Sweet Tooth (for each group of four students) 
One cup of sugar 
Cooking pan 
Measuring cup 
2 aluminum pie pans 
Cooking oil 
4 pairs of safety glasses 
2 - 4 hand lenses 
Wooden spoon

For Small Pieces (for each pair of students) 1/4 cup each of three different-sized sediment samples (small pebbles, sand and silt are good sizes) (these can usually be collected by visiting valleys and upland areas where the surficial materials are exposed below the soil.  Be sure no soil is included.  Collected sediments can be sieved in advance to separate the various sizes). 
3 paper plates 
Magnifying lens 
Clear plastic one-liter container with a cap (such as an empty shampoo bottle) 
Metric ruler 

Connecticut Rocks

Personal Favorites

Student Sheet

At Home

Find the rock you consider your favorite.  It could be a rock you've had for a long time, or one you choose today for this activity.

Your FAVORITE ROCK for this activity should be one that you have found at home or nearby.  You must have found YOUR ROCK in the town where you live and go to school.


On a 5x7-index card, describe your FAVORITE ROCK.  Tell why you chose this rock as your favorite.  Write about as many properties as you can think of Use any equipment available in the classroom to quantify some of your rock's properties.  Write your name on the card.

Punch holes into your card and tie some yam through it so you can wear the card around your neck.

Your teacher will assign a number to your rock and label your rock with its number.  Place your FAVORITE ROCK into a box with all of the other favorites. 
Without looking at the collection, each student will select one of the favorites.

Each student will try to reunite the FAVORITE ROCK selected from the box with its FAVORITE OWNER by matching the rock to its written description.

When each student is satisfied with the match selected, the class will learn which matches are correct and which ones are incorrect.  A few of the descriptions of the correctly identified FAVORITES will be read as well as a few of those incorrectly identified.  Students should discuss aspects of the various descriptions that either helped or hindered accurate identification.

All FAVORITE ROCKS should be reunited with their FAVORITE PEOPLE for the remainder of class. 

A Rocky Start


By doing this activity, you will begin to understand the problems faced by geologists as they have established criteria for classifying rocks.


(For each group of two or three students) 
One set of 10-12 rock samples 
One hand lens or magnifying glass for each student

(For the entire class) 
Several triple beam balances or other instruments that measure mass 
Assorted graduated containers of various volumes and shapes for finding volume 


1.     Form groups of two or three students. 
2.     Each group brings a tray of 10-12 numbered rock samples to its workstation. 
3.     Label index cards with the numbers of each of your rock samples. 
4.     Use your skills of observation and the equipment provided to write a list of properties of each rock sample on its corresponding index card. 
5.     Together with your partner(s), place your samples into groups according to a set of criteria that you agree to.  You must divide your samples into at least three groups, but you cannot form more than five groups. 
6.     Write a detailed record that describes the process by which your group divides the samples into categories. 
7.     As each group describes the categories of rocks they have formed to the entire class, each of the other groups should record the criteria that appear in more than one group. 
8.     All of the groups should compile a set of class criteria and record it on a poster complete with appropriate diagrams or illustrations, 
9.     The posters created by several classes can be displayed together with a set of rock samples so that comparisons of similarities and differences can be made. 

Rock Groups

By completing the previous activity, you and your partner(s) established a set of criteria by which to place your rock samples into groups.  You discovered criteria in common with other groups and agreed to a set of criteria your entire class can use to sort rock samples.

Scientists have chosen a set of criteria to classify rocks that is based on the ways in which rocks form. 
Rocks are classified according to their origin into three major groups -

Remember that the Earth's crust is made entirely of rocks and minerals.  We can see some rocks at the surface, while the rest of the rocks that make up the crust lie beneath the soil or under water.  All of the solid rock that forms the crust is calledbedrock.

Even though rocks seem like extremely permanent structures, it is important to understand that rocks exist in a cycle of change.  All the rocks you can see once existed in some other form and will be changed to yet other forms in the distant future.  At one time, all rock material was a liquid called magma.  When the liquid hardened, either above or below the surface, it formed igneous rocks.  Igneous rocks may be changed into either sedimentary or metamorphic rocks.

Changes into sedimentary rock always begin at the earth's surface wherever erosion and weathering begin to break rock into its mineral particles by ice, water, and wind.  Sedimentary rocks may become buried so deep that they melt and become an igneous rock.

Sometimes the crystals in buried sedimentary rocks or igneous rocks are rearranged while the rock remains solid resulting in the formation of metamorphic rocks

Igneous Rocks


The name igneous comes from the Latin word ignis, which means fire.  The Romans believed that Vulcan, the god of fire, had sent liquid rock to the surface, so they called the resulting eruptions volcanoes in his honor.  Remember that not all magma reaches the surface.  Much of it hardens below the surface.

Rocks melt at temperatures above 8000 C at depths below 25 kilometers.  Near melting conditions only a slight change in pressure or temperature is needed for rock to melt.  Either lowering pressure or raising temperature may cause the rock to melt.  Pressure could be lowered if a crack develops in the crust.  Temperatures may be raised if large amounts of radioactive materials are present or if a heavy blanket of sediment accumulates at the surface, such as at a delta.


Some magma moves upward rapidly along the cracks in solid rock and either flows out on the earth's surface or explodes out of a volcano.  Magma that reaches the surface cools quickly.  The difference in cooling rate determines the texture of the igneous rock that forms.  Slow cooling produces the large crystals of coarse-grained rocks, while rapid cooling produces the smaller crystals of fine-grained rocks.

Sometimes molten material cools too rapidly to allow the formation of any crystals, resulting in volcanic glass.

Occasionally, magma cools so quickly that gases are trapped within the rock.  After the gases escape, the rock is full of openings.  Pumice is a rock of this type.  Because of its many openings, pumice is lightweight enough to float on water.

Porphyries are igneous rocks which contain two or more different grain sizes because large crystal formed underground are carried to the surface by magma which completes its cooling above the surface.

Cooling rate also depends on the amount of magma, with large masses cooling more slowly than small masses, even at the same depth.


Rocks are made up of minerals that in turn are composed of the eight most abundant elements, namely oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium.

Oxygen and silicon are the most abundant of these elements.  They join to form a unit called a silicate tetrahedron that combines with one or more of the other elements to form the minerals found in igneous rocks.  All igneous rocks contain one or more of the silicate minerals.

Connecticut has a fine-grained igneous rock basalt, formed when liquid lava flowed out on the ground 200 million years ago and cooled quickly.  Three coarse-grained igneous rocks found in Connecticut are granite, pegmatite and gabbro, which formed way below the surface of the Earth, where the magma cooled very slowly.  Our granite is about 600 million years old and the gabbro about 480 million years old.  The pegmatites are of various ages.  Both have become somewhat metamorphosed, so are really metagabbro and granitic gneiss now. 

Cool Rocks


Some igneous rocks form by the cooling of magma that remains beneath the Earth's surface.  Other igneous rocks form when magma reaches the earth's surface.  This activity will show you some differences in the structure of those two kinds of igneous rocks.  See if you can observe what those differences are and what conditions cause them.

Imagine that the molten substance you will be working with 
in this activity is magma.


For the entire class:

Votive candle with holder (small aluminum foil dish) 
2 oz. salol crystals 
Ice cubes (2 cubes per team of four students) 
(store in a cooler or a freezer) 
2 metal spoons 
Quarter-teaspoon measuring spoon 

For each team of four students:

2-4 hand lenses 
Paper towel 
2 paper or plastic cups (2-3 oz.) 
2 votive candles with holders (aluminum foil pans) 
2 metal spoons 
2 lumps of modeling clay 
4 pairs of goggles


Part A

1. In each team of four, two pairs of students should place a small amount (less than 
1/8 teaspoon) of salol on a metal spoon. 
2. Melt the salol by holding the spoon more than an inch above a flame. 
3. Remove the spoon from the flame. 
4. Add a few grains of salol as "seed crystals". 
5. Prop up the spoon handle against a small lump of clay so the spoon stays level. 
6. Observe the crystals with a hand lens and draw what you see.

Part B

1. In each team of four, re-melt the crystals in one of the spoons. 
2. Rest the bowl of this spoon on an ice cube. 
3. Observe the crystals with a hand lens and draw what you see.

Part C

Repeat parts A and B, recording the time it takes for crystals to completely form.

Part D

Put two or three drops of melted salol on a glass or plastic microscope slide, and watch crystal growth with a microscope.

(Hint: If you want to save the salol for reuse, put plastic wrap on the slide before using it.  After the salol crystallizes, it will peel off the plastic wrap easily.)


Which "magma" sample completely crystallized faster? 
Which one produced larger crystals? 
Did the crystals you observed have angular, sharp-edged shapes, or were they more rounded and smooth?

Remember that igneous rocks form when magma cools.  Observe some igneous rocks samples in a classroom collection.  Why do you think some samples are made up of small crystals and others are made up of large crystals?  What conditions could lead to the formation of crystals of different sizes in the various kinds of igneous rocks?

Just as you have observed in your experiment, geologists also have determined that when magma cools very slowly deep inside the earth, igneous rocks with large crystals form.  When magma emerges above the earth's surface as lava, it cools quickly, forming small crystals. 

For Geologists with a Sweet Tooth


You know that some igneous rocks form when molten rock solidifies above the surface of the earth.  By doing this activity, you will observe a model of the processes that produce rock by very quick cooling. 

Materials (for each group of four students)

One cup of sugar                              Hotplate 
Cooking pan                                     Ice 
Measuring cup                                 4 pairs of safety glasses 
2 aluminum pie pans                        2-4 hand lenses 
Cooking oil                                     Wooden spoon


1. Observe a few sugar crystals with a hand lens.  Diagram what the sugar looks like in your data table. 
2. Measure one cup of sugar and place it in the cooking pan. 
4. Place the pan on a hotplate and heat the sugar until it has melted completely. 
5. One team member should stir the heating sugar constantly with a wooden spoon.  Another member should write a description of the melting sugar on your data sheet. 
 The third member should fill one of the pie pans with ice and place the other pan on top. 
 The fourth member of your team should pour a small amount of cooking oil in the pan on top of  the ice and swirl it around so that the entire bottom of the pan has a thin film of oil. 
6. Heat the sugar until it is completely melted and foam appears.  Pour it into the pie pan on top of the ice. DO NOT TOUCH THE HOT LIQUID. 
7. Observe what happens and write a description on your data sheet. 
8. After the hot solution has cooled, break off a piece and observe it with a hand lens.  Diagram what you see. 

What types of igneous rocks have your two sugar solutions created models of ?

Choose rock samples from among a classroom collection that have textures resembling those of your models.  Use available books to identify those samples. 

Sedimentary Rocks

Sedimentary rocks cover 75 percent of the earth's surface even though they account for only about five percent of the volume of the earth's crust.  If all sedimentary rocks were spread evenly over the earth, the layer would be only about three kilometers thick.  An igneous rock layer would be about 25 kilometers thick.

Sedimentary rocks can usually be distinguished from igneous and metamorphic rocks because they form in layers.  A sample usually breaks along layered surfaces.  Another key feature of sedimentary rocks is that they can contain fossils.  Igneous rocks never contain fossils, and fossils are only rarely found in metamorphic rocks.


Sedimentary rocks form at or very near the earth's surface, where rock particles are carried by wind, water, and ice and deposited on riverbeds, lakes, beaches' deltas, and the oceans.  Over time the weight of the upper layers of sediment squeezes those below, reducing pore space between grains.  Minerals deposited from ground water cement the particles together, forming solid rock.  The type of fossil found in a sedimentary rock is indicative of the rock's origin.  A marine fossil, for example, suggests that the sediments were deposited in the sea.

Grain Size

Grains in sedimentary rock exhibit a huge size range, from boulders to minute particles of clay.  Coarse-grained rocks have fragments easily seen with the naked eye, and include conglomerate, breccia, and coarse sandstones.  Medium-grained rocks have grains you can see with a hand lens and include finer-grained sandstones.  Fine-grained rocks include shale, clay, and mudstone.

Grain Shape

The shape of the grains in a sedimentary rock is a clue to how far the sediment was carried during erosion.  Sediments deposited near their source are angular and many different sizes.  Those sediments carried greater distances by water are more rounded and are sorted into sediments of similar size. 

Small Pieces, 
Even Smaller Pieces, 
Pieces Too Small to See


These activities will give you a chance to investigate some of the different types of sediment that make up sedimentary rocks.  You will experiment with processes and materials that model the formation of sedimentary rock.


For each pair of students:

1/4 cup each of three different sediment samples 
3 small paper plates 
Magnifying lens 
Clear plastic one-liter container with a cap (such as an empty shampoo bottle) 
Metric ruler

Part A

1. Measure about 1/4 cup of one of the sediment samples from one of the containers provide 
  by your teacher. 
2. Pour the sample onto a small paper plate. 
3. Record the sample number on the plate. 
4. Repeat steps one and two with two additional samples. 
5. Examine the samples with a magnifying lens and try to draw what the individual grains 
  look like.  Pay attention to shape and relative size of those grains. 
6.  Feel the texture of each sample and write a description under each diagram. 
7.  Label each diagram with its corresponding sample number. 
8.  Fold each of the paper plates around the sediment samples and pour all of the samples 
     into the clear plastic container. 
9.  Cap and shake the container until the three samples are thoroughly mixed. 
10.  Add water to the sediment samples, filling and recapping the container. 
11.  Shake again until the water and sediments are thoroughly mixed. 
12.  Label the container with the numbers of the three sediments it contains. 
13.  Set the container aside and leave it undisturbed until all of the sediment has settled.

Part B

1. When settling is complete, diagram the container and the sediments it contains. If you notice layers, pay attention to drawing their correct thickness. (Use a ruler, and measure to the nearest tenth of a centimeter).  Notice relative grain sizeamong the layers. Color your diagram to approximate the sediments. 
2. Label the diagram with the sample numbers.


I . Are the colors of the three sediment layers very different from each other or not very different?

2. What about the textures of the three sediments?  Are they very different, or are they very similar to each other?

3. Compare the grain size of the three samples.  Sketch the layers that formed in your container.  Label the layer with the smallest grains with a #I, the layer with the medium-sized grains with a #2, and the layer with the largest grains with a #3.

The three sediments you have been experimenting with are called gravel, sand and clay.  They form as a result of the weathering of existing rocks and minerals that are exposed to wind and rain, heating andfreezing at the surface of the earth. 
Sometimes, materials formed by weathering are transported and deposited as sediments at the bottona of rivers and streana, or near the places where rivers empty into larger bodies of water, including oceans.

Accumulated sediments become very heavy, compressing the sediments underneath them when the deposits become very thick.  That is how sedimentary rocks are formed.

One of the most distinguishing features of sedimentary rocks is their layering.  Your experiment demonstrates the way in which sediments tend to settle out of water in layers.

The individual grains of sedimentary rock tend to be rounded, not sharp-edged like the crystals of igneous rock.

You probably noticed that sand, silt, and clay differ most in grain size and mxture, but not much in color.  Sand is the sediment that has the largest grains and the coarsest textures Grains of sand can easily be seen with the naked eye.  The medium-sized grains in your container are silt.  You need a magnifying lens to see the individual grains of silt.  The finest grained sedimenty you experimented with is clay that has grains so small that, even with a magnifying lens, they cannot be distinguished from each other.

Scientists have set very specific limits for the grain size of sand, silt, and clay as well as other sediments.  Grains of clay are less than .002 mm in diameter.  Silt can be up to .05 mm in diameter, and sand grains can be up to 2 mm in diameter.

4. Write a paragraph that describes the procedure of this experiment and summarizes the results in terms of grain color, texture, and size. 

Metamorphic Rocks


Metamorphic rocks form when rocks are heated under pressure, but not heated enough to melt.  All metamprphic changes take place while the rock is in a solid or plastic state.  Metamorphism takes place at temperatures ranging from 1500 C to about 8000 C and generally where rocks are deeply buried in the Earth.


Metamorphism may be either regional or contact.  Regional metamorphic rocks such as slate, schist, and gneiss found in mountain-building regions where both heat and pressure cause changes in the rock over large areas.  Many regional metamorphic rocks are foliated, meaning that the minerals are forced by pressure to become aligned.  Foliation is the most important feature for identifying metamorphic rocks.  Contact metamorphic rock like form when direct heat alone changes rock.  This happens close to areas where there is magma.  Contact metamorphic rocks have a crystalline structure in which the minerals are randomly arranged.  This type of metamorphism may occur near the Earth's surface, as well as at depth.

Grain Size

Grain size sometimes indicates the temperature and pressure conditions to which the rock was subjected.  The higher the pressure and temperature, that coarser the grain size.  So slate, which forms under low pressure, is fine-grained.  Schist, formed by moderate temperature and pressure, is medium-grained, and gneiss, formed at high temperatures and pressures, is coarse-grained.

Mineral content

The presence of certain minerals in a rock sample can help to identify the rock.  Gamets, for example, form in gneiss and schist, although they are also found in the igneous rock pegmatite.  Garnet is the Connecticut state mineral.  Kyanite, staurolite and sillimanite (which was named for the famous Connecticut geologist Benjamin Silliman) are only found in metamorphic rocks.

Your teacher will provide you with exercises about metamorphic rocks. 

Connecticut Rocks Regroup

The rock samples you have been working with include the most common rocks 
found in Connecticut.  Among them are examples of all three-rock types - igneous, 
sedimentary, and metamorphic.  Look again at the set of samples you used in the 
Rocky Start 

Working in pairs, 
and using what you have learned about rock types and how they are formed, 
try to categorize Connecticut 's Top Ten rock samples into the 
three major rock types -

igneous, sedimentary, and metamorphic.

Then learn the identity of the individual rock samples by reading the descriptions and 
examining the photos provided by your teacher. 
Match each sample to the description that you think corresponds to it. 
Ask your teacher to check your results. 

Each pair of students should mix up their samples and identifications, 
and then trade sets with another team 
for more practice with identifying 
Connecticut's Top Ten. 

Returning Favorites

All students should get reacquainted with their 
and try to correctly identify the rock 
using any available information and resources.