While the ground beneath our feet may seem solid and stable, our Earth is actually an amazingly dynamic and fluid planet. Huge sections of the crust, called “plates,” are constantly on the move, spreading apart from each other at some places like under the Atlantic ocean, sliding past each other at other places like the San Andreas Fault, and crashing together at still other places to lift up mountains like the Himalayas. This unit will teach you about such processes, the definition of a rock, and how rocks of different sorts are formed by earth processes.
Activity 1. What is a rock.
Learn the definition of a rock and the three rock types (igneous, sedimentary, and metamorphic). Collect at least one of each of the three types of rocks.
Our earth is made of huge segments, or plates, that are constantly on the move, and as they move about, they help to recycle rocks and to create the processes and conditions that lead to igneous, sedimentary, and metamorphic rocks Make a poster showing the rock cycle. In the poster, include specific examples of the different sorts of rocks you might find along different parts of the rock cycle.
Activity 3. Igneous rocks.
|Igneous rock can be made on the surface of the|
earth by volcanic eruptions. Drawing by Jack
Shimon, CSMS Pebble Pup
b) make a plaster or clay volcano and set it off for your fellow club members; or
c) make an igneous rock collection of three or more different types.
Activity 4 Sedimentary rocks.
Learn about wind and water erosion and deposition and chemical precipitates and evaporates in order to understand how sedimentary rocks form. Then do one of the following activities:
a) make sandstone, conglomerate, and breccia and create a geologic column of these in a milk carton;
b) make a plaster or clay volcano and set it off your fellow club members;
c) make an igneous rock collection of three or more different types.
|A sedimentary rock. Drawn by |
Jack Shimon CSMS Pebble Pup
|Rivers deposit sediments that ultimately become sedimentary rocks.|
Drawing by Jack Shimon
Learn about “parent rocks” and the formation of metamorphic rock due to heat and pressure. Then do one of the following activities:
a) using clays of different colors as your “parent rocks,” make a metamorphic rock with pressure and heat by twisting and rolling clays together and then baking them in an oven;
b) make a metamorphic rock collection with three or moer different types
Insturctions to earn badge: complete one of the above activities to earn your merit badge on Earth Processes in each group of the three rock types. The easiest way to complete this badge is to look for these rocks on a collecting trip, trade with other pebble pups, or buy them. If you wish to do the other items to earn the merit badge, place contact me for detailed insturctions.
|A metamorphic rock. Drawing by Jack Shimon|
CSMS Pebble Pups
What is a rock?
A mineral is an inorganic chemical substance created in nature. “Inorganic” means it is not alive. Minerals often produce crystals, and a particular type of mineral always has the same chemical make-up that gives it a distinctive crystal form and colors. Minerals are the individual units or building b locks that, brought together, make up a rock. Rocks are inorganic solids from the earth’s crust that are made up of one or more minerals. To think about this a bit, stop and think about the people in our rock club. Everyone in the club represent an individual mineral. You have boy members, girl minerals, mother and father minerals, etc. Scattered around town, each is an individual, but when you bring them together in the same room, the individual boys and girls and parents become something new: a rock club. Just so, when individual minerals come together in a group, they create a rock.
Granite is a good example for showing how rocks are made of collections of minerals because crystals of the individual minerals making granite are especially large and visible as compared to some other types of rocks. Although different types of granite will have different combinations of minerals, most granite is made of the minerals feldspar, quartz, mica, and hornblende. The quartz will tend to be clear or milky and shiny like glass. The feldspar might be white, gray, or pink and somewhat dull. The mica will appear as silver or black glittery flakes. And the hornblende will appear as black specks. Look as a specimen of granite under a magnifying glass to see the different types of minerals in order to gain an appreciation of how a rock is made up of different minerals that have grown together.
Rocks are divided into three groups:
1. Igneous rocks cooled and crystallized from hot, molten magma, either on the surface of the earth or deep below ground. “Igneous” is derived from the Latin word igneus, meaning fire.” Examples of igneous rocks your kids might collect include granite, basalt, rhyolite, obsidian, gabbro tuff, andesite, pegmatite, or pumice.
|Fossils such as this |
trilobite may be
found in sedimentary
(art by Lauren Ingalsbe)
3. Metamorphic rocks are pre existing rocks that have been altered by erxtreme heat and/or pressure to create a rock with a new form and mineral structure. “Metamorphic” is derived from the Greek word metamorphosis, which means “to change” or “to transform.” Examples of metamorphic rocks are marble, gneiss, slate, schist, quartzite, soapstone, greenstone, and serpentine.
On Earth, rocks are constantly moving through a cycle of formation and change through processes involved with plate tectonics. The trust of the earth is divided into a number of plates that float and travel over the mantle. Much of the earth's seismic activity (earthquakes, volcanic eruptions, mountain building) occurs at the boundaries of these plates, where plates collide, diverge, slide past one another, or where one overrides another. In the process, new rock is formed, old rock is worn down and re-deposited as sediment, and other rocks are changed through heat and pressure. You can use various types of rocks to illustrate this rock cycle.
Igneous rocks formed from hot, molten magma, either deep underground (e.g.,
granite) or extruded onto the planet's surface (e.g., basalt). Igneous processes can form volcanoes and mountains that lift land up and create new land.
Sedimentary rocks, on the other hand result from processes that wear the earth down. Gravity, combined with the weathering properties of wind, rain, and freezing, disintegrates rocks, breaks them into smaller components, and transports them into valleys and basins as gravel, sand, or mud, where they pile up in layers and eventually harden into the sedimentary rocks known as conglomerate, sandstone, and mudstone or shale.
Sometimes, igneous and sedimentary rocks get buried under other rocks and get caught up into immense forces involved in plate tectonics and mountain building. When this happens, these rocks get heated and squeezed, and the pressures can change their structures and transform them into whole new rocks, known as metamorphic rocks. These include rocks such as gneiss, schist, slate, or marble. Here are some illustrations of how rocks move through a "rock cycle":
Granite is an igneous rock that hardened and crystallized from molten magma deep beneath the earth. You'll see bits of crystallized quartz in granite. When granite weathers, these quartz crystals get worn down into grains of sand. When deposited in a valley, lakebed, or ocean, sand can harden into the sedimentary rock called sandstone. If the sandstone is buried and subjected to heat and pressure, it will transform into the metamorphic rock called quartzite.
Also, the bits of flaky mica and the feldspar in ligneous granite can get worn down into silt and clay. When that hardens, it becomes sedimentary shale. And when shale is
subjected to heat and pressure, the original mica re-crystallizes to form flat, platy layers of metamorphic slate or schist.
The following are common igneous rocks that kids may be able to collect if they live in the right area of the country, or that they may be able to purchase from rock dealers, or that they may be able to trade through the mail as a club project with kids in other AFMS/FRA clubs who live in areas where igneous rocks are common:
• Andesite is a gray to black volcanic rock ,with a high silica content that commonly erupts as thick, sticky lava flows from stratovolcanoes, such as those in the AndesMountains, which gave this igneous rock its name.
• Basalt is generally a hard, dense, heavy, dark gray or black rock formed from magma that flowed out of a volcano or vent in thick streams or sheets. Basalt can come in a variety of forms. A' a (pronounced "ah-ah") is variety that cooled with a jagged, rough and rubbly surface. Pahoehoe (pronounced "pah-hoi-hoi") cooled with a glassy smooth hummocky or ropy texture.
• Gabbro is a dark (often black), coarse-grained, intrusive igneous rock chemically equivalent to basalt but that cooled deep beneath the Earth's surface, resulting in large crystal structures within the rock that sparkle in the light.
• Granite cooled from magma deep under the earth and as a result usually has large mineral crystals all grown together. Depending on the type of granite, these minerals might include quartz, feldspar, mica, olivine, etc.
• Obsidian is a heavy, smooth, and shiny volcanic glass rich in iron and magnesium that cooled very quickly during an eruption, so quickly that crystals didn't have time to grow, thus resulting in glass. Chemically, it's often identical to pumice, which makes it terrific to use for compare-and-contrast with pumice.
•Pegmatite is a very coarse-grained igneous granite consisting of quartz, feldspar, and
mica and commonly also containing large gemstone crystals such as tourmaline,aquamarine, and kunzite. Pegmatites form as a magma that cools quickly after intruding as a dike or sill into other rock.
• Pumice is formed from magma that shoots lout during a particularly violent, explosive eruption. Gases dissolved in liquid magma expand rapidly during the eruption, making pumice extremely frothy (like froth created when you shake a soda can and open it). Millions of tiny gas bubbles leave cavities shot through pumice, making it extremely light-so light that it can often float on water!
• Rhyolite is often a banded light-colored, fine-grained rock that formed when thick, sticky lava flowed for relatively short distances.
• Scoria is similar to basalt, but whereas basalt usually flows in a thick, fluid layer from a volcano, scoria is shot into the air as a cinder during explosive eruption events. Thus, like Swiss cheese, it's peppered with holes from gas bubbles, making it much lighter than basalt.
• Tuff is volcanic ash and cinder that settles while still quite hot and becomes welded and compacted into layers of coarse, often lightweight rock that's usually white or gray or cream in color.
The following are common sedimentary rocks that kids may be able to collect if they live in the right area of the country, or that they may be able to purchase from rock dealers, or that they may be able to trade through the mail as a club project with kids in other AFMS/FRA clubs that live in areas where sedimentary rocks are common:
• Breccia is a clastic sedimentary rock composed of cobble- and pebble-sized rock
fragments that are sharp and angular, indicating that the rock fragments had not been transported very far before being deposited and buried.
• Coal originated from compressed vegetation, often derived from swamps, that was buried rapidly in thick masses. High in combustible carbon content, coal-burning
facilities are the largest source for generation of electricity.
• Conglomerate is a clastic sedimentary rock formed by the cementing of rounded cobbles and pebbles that have been worn smooth during transport in streams, rivers or ocean shores.
• Coquina is similar to conglomerate, but rather than being formed by rounded cobbles and pebbles, it's formed by masses of broken seashells, coral fragments, and other biologically-derived materials that are poorly cemented together.
• Diatomite, a soft chalk-like sedimentary rock, is composed primarily of silica from the fossilized shells of billions and billions of microscopic diatoms, which are algal-like organisms at the base of the ocean's food chain. It has many industrial uses as a filter (you'll see it in hardware stores with pool supplies), a mild abrasive, and as filler (as in house paints); under high magnification, the individual diatom shells look like snowflakes.
• Gypsum is a chemical sedimentary rock precipitated from highly saturated salt waters that left behind thick deposits of sulfate hemihydrate. Gypsum is the main
ingredient in plaster of Paris and is also used in drywall, so you may well be surrounded by gypsum at this very moment.
• Limestone is a type of non-clastic, chemical sedimentary rock also called calcium carbonate because of its high content of calcium. It generally forms as a limy ooze
precipitated on the ocean floor and includes shells from marine animals.
• Sandstone is a clastic sedimentary rock formed from the cementing of sand-sized grains, often from minerals in groundwater, along with pressure.
• Shale is one of the most common sedimentary rocks. It's composed of silt, mud, or clay that has been compacted to form a solid rock.
• Travertine is a form of calcium carbonate (like limestone) deposited through the action of water, such as mineral-rich springs. It's often soft and beautifully banded,
making it a favored sculpting stone. It's also sometimes called onyx and alabaster..
The following are common metamorphic rocks that kids may be able to collect if they live in the right area of the country, or that they may be able to purchase from rock dealers, or that they may be able to trade through the mail as a club project with kids in other AFMS/FRA clubs that live in areas where metamorphic rocks are common:
• Gneiss (pronounced "nice") is a "high grade" metamorphic rock derived from various sources (e.g., granite, shale, conglomerate, etc.) that were subjected to intense heat and pressure, heat so high that the rock nearly melted to a magma, resulting in minerals that drew together in distinct banding patterns under the high pressure.
• Greenstone is a fine-grained massive metamorphic rock with a dull luster that comes in varying shades of green; in California, it's associated with gold-bearing veins in the Mother Lode mining country.
• Marble is limestone that has been altered through metamorphic action. Soft, easily carved, semi-translucent, and capable of taking a polish, it's often used by sculptors and builders. Marble comes invarious forms, depending on the elements contained in its parent rock. For instance, limestone marble contains mostly calcium carbonate and may have interesting veining (or "marbling") with colors due to different mineral impurities. Dolomite marble had a parent rock of dolomite, which is similar to
limestone, but with magnesium in addition to calcite as a constituent mineral. And strong>mariposite (named after Mariposa, California, where it occurs in abundance) is a form of dolomite marble with a high green chromium muscovite mica content that gives it a distinctive green marbling.
• Quartzite is a massive, medium-grained metamorphic rock with a sugary texture often derived from sedimentary sandstone.
• Serpentine is a fairly soft metamorphic rock that may be waxy to the touch and has apple-green to black, mottled coloring that can look like serpent scales. It's the
official California State Rock.
• Slate is a "low grade" metamorphic rock (meaning it was subjected to only low heatand pressure) formed from sedimentary shale; it splits, or cleaves, in flat surfaces, and has been used as roofing shingles and blackboards.
• Soapstone consists mostly of an impure, massive variety of talc. Soft, with a pearly sheen, it's a popular sculpting material, but has many other uses, such as in the manufacture of laboratory tabletops, firebricks, and electrical apparatus due to its resistance to heat,electricity, and acids.