Feb/01/2016
Crystals / Earth Science / kitchen science / Minerals

Curious About Crystals?

Crystals, crystals everywhere, even those you can eat! All year long you and your child can explore crystals in the kitchen including sugar and salt. And, oh my, crystals in bling! Natural diamonds, sapphires, and rubies are all types of crystals. Not into bling? Consider exploring the world of mineral crystals. There are over 4000 of these, so plenty to keep a child busy.

As you may have determined, the term crystal is associated with a variety of things we would not typically group together. But yet, they are all crystals because they share a similar characteristic.Crystals are interesting for younger children to examine, but this particular post may be geared for slightly older or elementary school-age children.

For parents, let’s start with basics and some important distinctions. If you aren’t really into the specifics yet, skip to the Experiment section and start making your own crystals. If your child finds these interesting, perhaps you’ll be inspired to return and read the following for a deeper explanation of what crystals are.

Here goes. A crystal is the end result of combinations of atoms that form a naturally occurring, near perfect, three-dimensional (3D) recurring arrangement. This ordered atomic structure is called a crystal lattice and a single building block of this lattice is called a unit cell. The external forms we are all familiar with are the result in the different geometries defined by the arrangement of crystal faces. Examples of these would include natural diamonds, salt, and even rock candy.

Precious gems you see in the jewelry store like diamond, sapphire, emerald and ruby have naturally occurring crystal shapes and when they form in nature they are true minerals. However, not all gems are natural as they can also be grown synthetically in a laboratory. Additionally, skilled gem cutters have carefully polished the sparkly crystal faces you commonly see in cut stones. The complex geometry of these cut faces may not reflect the underlying crystal lattice of the original mineral; however, at the atomic level, the geometric arrangement of atoms is identical in both synthetic and natural minerals.

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Minerals are by definition inorganic and all minerals can form crystals under the right conditions. However, not all crystals are minerals. Sugar is an organic chemical compound or molecule containing carbon, hydrogen and oxygen, but sugar and other organic compounds can form crystals under the right conditions.

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Lastly, the “crystals” hanging from grandma’s crystal chandelier are also not true crystals. Nor are the gemstones in most costume jewelry. These sparkly objects are made of polished pieces of glass. The crystal “faces” on these objects are not naturally occurring but have been artificially cut and polished just like the gemstones we mentioned previously. Although glass, just like the mineral quartz, is made of pure silica (SiO2), it does not have a repeating 3D atomic structure. Therefore, glass is not crystalline.

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So, now that we are straight on what is and is not a crystal, let’s get started exploring. Invite your child to examine existing crystals or make some of your own. Enjoy the interesting patterns and appreciate nature’s wonderful and often perfect creations.

 
 

Questions

What do crystals look like?

 

Are all crystals the same shape?

 

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Where can I find them?

 

How are they made or formed?

 

Can I make a crystal?

 

How can I tell if something is a crystal?

 

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Observe

Start with observing a readily available crystal or table salt. Pour some out, perhaps on black construction paper as a contrast. What do you see? Your child should notice the shape of the crystals and color. A magnifying glass will help. If she is looking at sea salt, there could be other elements in the mixture depending on how refined the salt is. Even regular table salt contains other elements, but should be about 97% sodium chloride. Salt can also be felt, tasted and smelled, or use all the senses when observing.

 

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The structure of the salt crystal is a simple cube making it a good place to start in thinking about the shapes or crystal structures. Notice its symmetry or the fact that the sides should all be about equal and edges should meet at right-angles to each other.

 

If you have a chance to go to a specialty grocery store, look at the variety of sea salts that have been “mined” for our use in the kitchen. If you don’t want to buy these, as they can be expensive, maybe peek at the jars examining variations in the size of the crystals and their color. If your child is interested in salt, take a look at my Salt activity page for other suggestions.

 

http://guidingcuriosity.com/start-with-salt

 

Other crystal geometries can be more complicated as you will see below, but you can begin by looking for basic shapes or triangles, cubes, rectangles and hexagons as a starting point and a good review of basic geometry. The external shape of a crystal depends on the elements it is made of, the conditions under which it grew, and most importantly its specific 3D crystal lattice. That is, the chemical elements available to make a crystal will largely determine its shape because there are a limited number of ways you can organize repeating 3D atomic structures or “unit cells”.

 

If your child is still interested in crystals, consider examining crystals in rocks. You may have to take a walk and collect some rocks with obvious crystals. Or, hopefully, you have a collection of rocks at home and can examine these. Every kid should have a rock collection!

 

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Rocks are formed with minerals, usually two or more. Minerals are the building blocks of the universe. Look for individual grains of quartz or flakes of mica, as these should be familiar and common mineral crystals in rocks. Can you see the crystal structure or shape? Maybe look for a characteristic flat surface referred to as a crystal face (or facet). Crystals are not always clear or transparent, so keep your eyes open for a variety of colors and even opaque minerals.

 

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If you have access to larger minerals with an obvious crystal shape, such as a piece of amethyst or a geode, again take a close look. What shape is it? Can you see two adjacent faces? If so, then what is the angle between them? Even though it is just a variety of quartz, amethyst is considered a semi-precious gemstone and you might be thinking that you are not going to buy expensive jewelry for your child to examine. But if you visit a gem and mineral show or a rock shop, you can buy inexpensive minerals that will prove instructive and fascinating.

 

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Here is an example of a site where you can buy those minerals on-line.

http://www.bestcrystals.com/kids3.htm

 

New mineral crystals are forming both on the earth’s surface and deep within. When looking at rocks or minerals, the crystals were likely created in one of four ways.

 

  1. The majority resulted when molten rock or magma cooled very slowly and under pressure. These are igneous rocks and one example would be granite. Granite contains several different minerals such as quartz, feldspar, and mica.
  2. Igneous rocks as well as other types of rocks, like limestone, shale or sandstone, can be transformed through high temperatures and/or pressures. This process is called metamorphism. Different temperatures, pressures and most importantly starting compositions dictate how the atoms combine into which particular minerals. Sometimes well-form crystals like garnets are a result. An analogy is like cooking a casserole. Recipes call for starting with different ingredients. You combine and mix these, then put them in the oven. After the ingredients have reacted with each other for a period of time while heating, something different and delicious comes out.
  3. A third process resulting in crystals is when hot fluids, mostly water containing a lot of dissolved stuff, find their way through rocks. Those fluids cool slowly, sometimes resulting well-formed crystals. Quartz veins are a good example. Hot gasses associated with volcanic areas can also leave behind crystals as the steam cools and the minerals precipitate.
  4. Lastly, surface waters like rivers and streams can carry a lot of dissolved solids and when these go into an internal drainage basin and evaporate crystals can be left behind. Think of the expansive salt flats near the Great Salt Lake.

 

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In the experiment section below, you can experience the process of crystal formation directly, with ideas for hands-on activities to create your own crystals. Most mineral crystals, however, take thousands of years to “grow.”

 

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Compare and Contrast

Compare the shapes of various crystals. All crystals can be grouped into one of seven different systems based on some simple geometric rules relating to the lengths and orientations of its crystallographic axes. What is an axis you ask?

 

Picture a cube. It is a six-sided object with all sides being squares. If you drew a line from the center of one side through the center of the opposite side, that would represent one axis.

 

diagram

 

You could rotate the cube on this axis and see four equal faces. Since there are three pairs of “opposite sides” you could do this three times. Hence, the Cubic (or Isometric) System has three axes and they are all of an equal length and perpendicular to each other. (Note: if the three axes went through the opposite corners, instead of the middle of the opposing faces, the crystal would still be in the Cubic System.)

 

The Tetragonal System has three axes, all perpendicular to each other; however, one axis is longer than the other two which are of equal length. Think of a tall box with a square top and bottom (or a square pyramid on the top and bottom).

 

The Orthorhombic System has three axes, all perpendicular to each other and all of different lengths. Think of a shoe box or cereal box.

 

You can easily illustrate this concept of a rotational axis to your child at home by locating some small cardboard boxes and using pencils or dowels as axes. Observe the similar shaped “faces” as they rotate by

 

The Hexagonal System has four axes. Three in one plane, each of equal length and oriented at 120-degree angles to each other. The fourth axis is perpendicular to this plane and of a different length than the others. Think of a tall cylinder with six equal (rectangular) sides and a long axis down through the center. Alternatively, the shape of a common six-sided hardware nut (as in nuts & bolts) would also in the Hexagonal System.

 

The remaining three Crystal Systems: Rhombohedral (or Trigonal), Monoclinic and Triclinic are geometrically a bit more complicated since not only do the lengths of the three axes vary but so do the angles between the various axes.

 

Here is a diagram showing examples of the seven basic Crystal Systems

 

mineral types

 

 

Here are two sites where you can print out some worksheets that can be cut and folded into a variety of 3D geometric solids.

 

http://www.senteacher.org/worksheet/12/NetsPolyhedra.html

 

http://www.fun-stuff-to-do.com/printable-shapes.html

 

Some of the folded 3D solids can substitute for real crystals. Obviously, cones, cylinders, and any 5-sided forms will not. Some of the prism shapes may have to be connected base to base to make a complete “crystal”. By using dowels as “axes” you can manipulate and classify most of these shapes into one of the 7 basic crystal systems. Marking the sides can help with this exercise.

 

Here is another site that provides trading cards of minerals. The information is helpful in determining what the mineral is and its characteristics. If you print the cards they can be examined and the facts associated with each mineral compared and contrasted.

 

http://www.kidsloverocks.com/pdf/TradingCards04.pdf

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Measure

Count the number of sides of any crystal. If you printed and constructed some of the 3D shapes mentioned, go ahead and number them or mark them up. Can you find matching “pairs” of faces that would represent two parallel faces pierced by the same crystal axis?

 

Measure the length of the sides if possible and the crystal is not too small. Measuring microscopic crystals is clearly not an option, but measuring the faces of the larger mineral crystals, such as amethyst or quartz crystals, is easy.

 

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Experiment

Grow your own crystals. Crystals are not alive, so the term “grow” refers to creating chemical reactions.

 

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Here are some options:

 

With the help of an adult, take a cup of water and bring it to boiling. Stir in 3 tablespoons of alum until it dissolves. Alum can be purchased in the spice section of your grocery store. Pour the solution of alum and water into a clean jar. Cover the jar loosely with plastic wrap and put it where it will not be disturbed. Check regularly. The hardest part about this experiment will be waiting. The water has to evaporate (thus the loose plastic wrap on top of the jar), and as it does so, the alum in the jar becomes more concentrated. With more alum and less water, the alum molecules will latch on to one another.

 

If a crystal doesn’t grow, try again. The solution must go into a clean jar. You may have to rinse the jar with a bit of the boiling water before adding the solution.

 

You can also use Epsom salts (magnesium sulfate) to grow salt crystals. Repeat the procedures above using about ½ cup of boiling water and ½ c Epsom salts. Completely dissolve the Epsom salts in the water, place the container in the refrigerator for a couple hours. Examine the results. What shape are the crystals that grew (should be long needles)? Can you sketch or draw the crystal structure? You can repeat this experiment with table salt. Remember that the shape of the crystal will depend on the chemical element in the solution. Based on observations of table salt crystals, predict what the final shapes will be.

 

You can also make growing crystals into a fun “make your own geode” project by following the instructions on this website by Martha Stewart.

 

http://www.marthastewart.com/343344/crystal-egg-geodes

 

 

The following are instructions for growing edible crystals or “rock candy”. Tie some cotton or wool string to a pencil or straw. Set the pencil or straw across the top of the glass jar and make sure that the string will hang down into the jar. The string should not touch the sides or bottom. Adjust the length of the string so it is close to the bottom but not resting on it. If the string does not hang straight, you may need to add a weight to the bottom. Often a paper clip is suggested for this purpose. Whatever you choose, make sure it does not contain toxins such as lead that could leach into the water.

 

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With the help of an adult, boil a cup of water. Once the water is boiling add sugar about a tablespoon at a time stirring until it dissolves. When the sugar no longer dissolves and starts to accumulate at the bottom of the pan, stop adding additional sugar. This should take approximately three cups of sugar. If the added sugar does not dissolve, you have a saturated solution. Do not continue to add sugar if you have reached saturation.

 

If you want colored crystals, stir in a few drops of food coloring. You can also add flavorings, such as Kool-Aid, lemon juice, or peppermint extract.

 

Pour your solution into the clear and clean glass jar. If you have undissolved sugar at the bottom of your pan, do not pour it into the jar. Position the pencil or straw over the jar and allow the string to dangle into the liquid. Set the jar somewhere where it will not be moved or disturbed. If you like, you can place a paper towel over the top of the jar so that nothing else can fall in.

 

Check on your crystals after a day. You should be able to see the beginnings of crystal growth on the string. Let the crystals grow until they have reached the desired size or have stopped growing. The longer you wait, the larger the crystals will be. When you are ready, you can pull out the string and allow the crystal to dry. You can eat them or perhaps share them with friends.

 

Take some older small toys, small rocks, or other disposable objects that you are willing to use to make a crystal sculpture. Place them in a pie pan. Mix about 4 tablespoons of salt with ½ cup of water. Stir the salt-water solution until the salt is dissolved. Pour this solution over the selected objects and place the pan in direct sunlight on a windowsill. Wait a few days, inviting your child to observe and talk about what he sees. You can add food coloring to the solution, or halve the recipe adding different colors to each half for a more colorful final sculpture.

 

 

 
 

Elaborate and Glossary

Visit a gem and mineral show in your area, or a rock shop that sells minerals. Examine the variations in the crystal structures that are obvious. Start a collection!

 

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Some crystals are used in electronics. Quartz crystals are commonly found in watches. These and other crystals vibrate at precise frequencies when an electric current is sent through. This characteristic makes them useful for keeping exact time. Quartz is a common mineral as well as one of the hardest. Here is a site describing other uses of crystals in science and engineering. Find your favorite crystal and see how it contributes to how we live.

 

http://scienceviews.com/geology/minerals.html

 

Some animals including ourselves can “create” crystals. Know anyone with kidney stones?

 

Buy a geode. Open it with a hammer (wearing protective eye gear) and take a look at the wonders inside.

 

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Find books in the library describing the work of scientists who study crystals and read about their stories.

 

 

 

Vocabulary

 

Crystal face

 

Axis

 

Unit Cell

 

Crystal System

 

Symmetry

 

Thanks,Tony!

Photos Courtesy of Shutterstock

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