Rock of the Week 2007/2008

I have a new favorite rock! Haley M., and Katey M. brought this little gem in from the beach. It's a sedimentary rock with a great fault in it. The layers in this sample were offset by less than a centimeter in the earthquake (left). On the flip side of the rock (right) the fault is not as pronounced, and there might actually be a second. The second really doesn't show in the image. It is located in the curvature of the rock on the right hand side. Nicely done ladies! Keep on walking those beaches!

This is Mr. Bertrand's (a retired social studies teacher who now spends his time scouring the country for "Rock of the Week" candidates) brought this piece of lava back from a location near Craters of the Moon National Monument in Idaho. As luck would have it, I was doing my igneous rock lab the day he brought in this sample, and it identicle to a sample I was using in the lab that I had misidentified as coming from Iceland. Nicely done Mr. Bertrand! Keep on scouring the country looking for those great samples!

This is a strange sample. The rock is a blend of very muted tans and pinks. The pinks are in a series of concentric circles inside of the sample! They look natural. I think the rock is metamorphic because of the amount of mica in it, but even that is open to debate. The rock comes from the Mt. Washington area of New Hampshire. Thankk you Mike K. for a great Rock of the Week!

I have been waiting since my return from the NSTA National Convention in St. Louis last April to do this lab. As soon as I saw it, I knew it was great! I belong to three lists, and had teachers from around the country send me sand samples for this project. I requested only sand from the Atlantic Coast, but I received it from all over the country. The Atlantic sand went into the lab, and the "other" went into the "Sand Hills" lab. Click here to read Caitlin's story about the Minot sand.

"This rock is sedimentary because it has layers. The earth was [weathered] and eroded, and the pieces flowed down a river. The pieces settled at the bottom of the river, and then more and more layers came, and were deposited. The layers were pressed down until the bottom layers turned to a rock. That is how this rock was formed, and it also explains the three different colored rock types. I got this rock in Arizona, near the Saguaro National Park. It is special because there are three rocks here in even layers. There is a distinct difference in the layers ranging from one color to the next." Steph. J.

This is one of the strangest samples I have ever been given. T.J., the student who gave this to me, said he thought it was a small skull with pieces of material attached. At first glance, I thought it was the skull of an extra terrestrial. It probably is a piece of neatly weathered coral. You be the judge. Here are the facts. "I found [the rock] in the Bahamas. This is a sedimentary rock. I found the rock on February vacation on a small island called Hamburger Beach in Great Exhuma, Bahamas. On the bay side of the island is a burger joint, and on the the other side is the open Atlantic Ocean. This was one of the only spots that I went to that showed the open ocean directly (no reef in the way). On this side of the island were many interesting rocks along with many gigantic boulders, most of them with little crevices underneath. It was under one of these crevices that I found this [sample.] This rock is special to me because it shows a well preserved skeleton, and I can keep this part of history forever." T.J.

This is probably a piece of rhyolite. It formed very quickly from lava/magma cooling. It's felsic. Sometime after it was placed on the surface, something happened to it to give it that ring. Is the ring a mineral stain? Is it a stain left by an organism? "This rock is my favorite because of the orange ring in the corner of it. I found it while I was walking on Duxbury Beach." Rebecca M.

This was a true find! This fossil comes from Pennsylvania. When most people think of fossils they think of dinosaur bones, or fish, or petrified wood. There are other types. Picture a location where there is a body of water that comes and goes. During parts of the year it is dried. Mud cracks form. These are usually five-sided objects. Such is the case in this example that Lucas B's father generously donated to our fossil collection! Usually these areas get destroyed when the water comes back. But something unique happened here. A second type of material filled the crack, and it was preserved. This tells us that this area was once on the surface of the earth, and that water was present some of the time. Thank you Lucas!

This was a true find! Every time I go to the beach, over the past 40+ years, I've always looked for unique stones. This one was the best! I show a film every year from the HBO series "From the Earth to the Moon," that contains a geologist who says that geologists are really storytellers. This tiny sample is probably one of the best examples of this story telling concept. Look at it! At first glance, it's a sedimentary rock. Probably a shale. The alternating bands of light and dark illustrate summer and winter. Then there is more! After all of those layers were deposited and turned to stone, an earthquake happened and created a minor normal fault in the rock! It doesn't get any better than that!

These are the fossil remains of a fish from the Green River Shale in Wyoming. I collected this fossil several years ago. Instead of falling onto an exposed surface, this fish settled into the quiet mud near the edge of a pond, and became a piece of history. 15 million years later, I was the first person to see this critter again, and expose it to the elements once again.

I collected these on a field trip out to Peddocks Island in Boston Harbor two summers ago. The shells are 440,000 years old. They are found in the cliffs that make up the drumlins found on Peddocks. The most amazing part of these shells is that they still exist. Drumlins are formed as glaciers advanced and encountered an object they couldn't move or destroy. Instead the ice flowed over the object dropping debris as it did so. Drumlins usually have a steep side, the side facing the ice, and a trailing side with a gentle slope.. That's a huge amount of destruction! Why weren't the shells ground into a powder? No one knows. Mr. Lindgren

This is a piece of coquina from Virginia. Coquina is an animal, and it's also a rock. From Florida up to Virginia these shells accumulate in huge piles turning into minireefs of dead animals that eventually turn to the sedimentary rock limestone. Why doesn't this happen here? Hint: The number of shells is probably the same in both locations.

This is a piece of coral from a coral reef. I got this on a trip to Bermuda over the summer. There were a lot of coral reefs when I went snorkeling in the bay. Many fish would feed off the reef. Coral is an animal. We are looking at what might become a sedimentary rock called limestone. Bridget B.

This rock is metamorphic. It's anthracite coal. Anthracite coal began its life as a tree in a forest. The tree died and was first converted into peat, then bituminous coal, and finally crushed under heat and pressure to form anthracite. This is my favorite rock because my parents gave it to me when I was born. It comes from the Titanic. I have it in a special case with a plaque describing its origin, and my name! Chris M.

This rock is mostly sedimentary, and part igneous. It was formed over a long period of time. It started out as a dolomite [the rock that is found under Niagara Falls] Then a volcano erupted and sent magma through the cracks in the dolomite. Then the magma cooled and formed the mineral quartz. This rock was found in St. Lawrence, New York. This rock is special to my mom. It has been with her since she was eight years old. Her old neighbor in New Jersey was a rock collector. When my mom was trying to do a rock project, her neighbor gave her a rock collection. This rock was in that collection. Maggie T.

About 300 million years ago, a warm shallow sea covered much of what is now Colorado. The sea was populated with tiny crustaceans whose hard shells protected them. The shells were made a mineral, calcium carbonate. The abandoned shells settled to the bottom of the sea forming many layers. As the sediment was covered, pressure gradually changed the layers to limestone. In a few places on earth, water, pressure, and heat changed the limestone deposits to a new rock, marble.

Where the earth's crust was hottest, it is pure white in color. About 60 million years ago, a dramatic volcanic upheaval elevated a massive dome of limestone and heat metamorphosed the limestone into marble. This dome, seven miles in diameter, is being mined at Marble, Colorado. Colorado marble was used in creating the Tomb of the Unknown Soldier at Arlington National Cemetery and the Lincoln Memorial in Washington, D.C., as well as many national buildings all over the United States.

"My rock is a sedimentary rock. It is a sedimentary rock because I noticed how many layers of deposits were built up, finally creatingthe rock itself. This rock is special because my entire family and I found it on a beach in Scituate." Julie R.

""My shark tooth is a fossil. I say this because my tooth was petrified. That happened when the tooth was replaced by non-living minerals making it into a sedimentary rock. A fossilized rock can be very, very old. It takes a long time for each of the minerals in the tooth to be replaced by non-living minerals one by one. Also think of how small a molecule of a mineral is, and how many molecules would be in a 10 cm tooth. My tooth was collected from a South Carolina river bed. I do not have evidence of that because I inherited it. I decided it came from South Carolina because of its color. The black of the enamel and root is very rare, and is typically found in a South Carolina river because of the chemical compounds found there. My shark tooth is very special, because it came from the mouth of a 60 foot 70,000 pound megalodon shark. That is quite exquisite and special. The megalodon had been around for 17 million years, and went extinct 1.6 million years ago. The black color of the tooth makes it even rarer

I am collecting sand samples from up and down the Atlantic Coast for a lab we will do sometime in the future. Along with sand samples, some of the folks are including rocks. The leaf is in a very fine, light colored shale. The leaf probably fell into a shallow pond, and was quickly covered many millions of years ago.

Rock of the Week

5/19/08