In some solids, the arrangements of molecules throughout the material are random. In crystals, however, the molecules are repeated in exactly the same pattern over and over again throughout the entire material. Due to their repetitive nature, crystals can take on strange and interesting shapes naturally. Students can observe the shapes of crystals firsthand by making their own via a saturated solution of copper sulfate or some other crystal-forming substance. They will know that their solution is saturated when a point is reached that no more solute will dissolve, even with further heating or stirring.
A wide variety of substances may be used to make the crystals, so you may want to decide on the substance that is most convenient for you, or even have different groups of students utilize different chemicals. Any of the following should be sufficient. Alum, a common ingredient for making pickles, can be found in the spice and herb section of the grocery store or purchased at some drug stores. Copper sulfate, which can be found at hardware stores, nurseries, or in science catalogs, is usually sold as a product that kills tree roots in septic or sewer lines. Borax is a laundry product that can be easily found at the grocery store and will make easy-to-observe crystals. Epsom salt, commonly used for a variety of purposes in many households, is another product that can be easily found, usually in drug stores or in grocery stores. Granulated sugar and table salt also create interesting crystals.
In order for your students to achieve optimal results, make sure they measure according to the directions, since more of a chemical does not always make better crystals. Also, when heating their solutions it is best to use saucepans that are glass or enamel because metal containers may react with the chemicals. Furthermore, it is preferable to use distilled or filtered water, although tap water usually works very well. To determine whether tap water will affect the crystals your students are making, perform the "ice cube test." If ice cubes appear cloudy, tap water will probably produce cloudy crystals, so they should use distilled or filtered water instead. Keeping the crystal growing experiments in an area with constant humidity and temperature will further help your students form the best possible crystals.
If your students are having trouble, there are several different variables you should check. For instance, if crystals do not form at all, they may be using too much water, not enough of the chemical, or the temperature or humidity may be unfavorable. If crystals form but are tiny, however, they may have too much of the chemical in proportion to the water or evaporation may be occurring too quickly. On the other hand, if crystals grow but get smaller or disappear altogether over time, then students should add more chemicals to the solution and begin again. As mentioned previously, cloudy crystals may be an indication that there are impurities in the water or in the chemical that is being utilized.
What will the students do?
Students will make crystals using one or all of the solutes listed in the materials section. For example, if students are making a copper sulfate solution, they will place 10 ml (2 tsp.) of warm water in a jar or other container and add 7 g (1 tsp.) of copper sulfate. They will then shake or stir the solution until the copper sulfate is dissolved. Afterwards, students should take a dropper, or a straw, and put one or two drops of the liquid in the center of a slide and place it where it will not be disturbed. Students will examine the slide the next day and record observations in their science notebooks.
Art - Before photography was widely used, geologists, astronomers, naturalists, and other scientists used words and drawings to inform each other about their discoveries. Have students pretend they are geologists and have them draw pictures of crystals as carefully as they can, including all details. Then, encourage students to color the drawings. The more detail they have included, the more colors they can incorporate. Students can compare these drawings to the actual drawings of birefringent crystals in Activity 16.
Writing - Have students imagine that they are spelunkers (cave explorers) and have them write about the kinds of patterns, shapes, and formations they would see. Students can include stories about stalactites and stalagmites. Also, if any students have visited caves (such as the Marianna Caverns, Luray Caverns, or Carlsbad Caverns), encourage them to share what they have seen to help others envision what caves are like. Ask students to illustrate their stories.
Reading - Either have students read or read aloud to them Gary Paulsen's The Legend of Red Horse Cavern (ISBN 0440410231). The adventure story about young people lost in a cavern could be a launching point to encourage students to do further research on caverns or to write their own stories.
Guest Speaker - Invite a gemologist to speak to the class, display some precious crystals and discuss how the crystals are cut to make them marketable. Try contacting a local jewelry store, geology club, or college or university department.
Historical Vignette: The Legend Behind the Hope Diamond
Perhaps the most famous gemstone in history, the blue Hope Diamond is 44.52 carats and is believed to be unlucky for its owner. Originally 112 carats when it was mined in India, the diamond was brought to France in 1668 by Jean Baptiste Tavernier. It was said to be cursed because a thief stole the diamond from the eye of a statue of the Hindu goddess Sita, wife of Rama. According to the curse, misfortune, unhappiness, and even death would come to anyone who stole the stone or took possession of it. Tavernier sold it to Louis XIV, who had it cut into a 67 carat heart-shaped stone and named it the Blue Diamond of the Crown. Tavernier was reportedly killed by wild dogs on his next trip to India.
Louis XVI and Marie Antoinette inherited the French Blue, as it was popularly known. In 1792, about the time of their executions, the French Blue and all of the other French crown jewels were stolen. Many of the jewels were recovered, but not the Blue Diamond of the Crown. There are reports that the diamond was re-cut to its present size by Wilhelm Fals, a Dutch diamond cutter. It is believed that he died after his son Hendrick stole the diamond from him. Hendrick later committed suicide.
In 1830 a 44.52-carat, deep blue, oval-cut diamond appeared in London. It was believed to have been the French Blue re-cut to conceal its identity. Henry Hope bought the gemstone and since then it has been called the Hope diamond. Many Europeans have owned the diamond, and many had similar tales of unlucky experiences. It was sold, for instance, to Evalyn Walsh McLean, a wealthy American, in 1911. After she bought the Hope diamond, her son was killed in an automobile accident, her husband died in a mental hospital, and her daughter died in 1946 from an overdose of sleeping pills. Following her death in 1947, Harry Winston, a well-known jeweler, purchased all of her jewels including the Hope diamond. He gave the gem to the Smithsonian Institution in Washington, DC, in 1958, where it has remained on permanent display ever since.
Narrative writing - Use the following as a narrative writing prompt: Diamonds are a type of crystal. The Hope Diamond is a very famous example of a crystal. Think about what happened to people who have owned the Hope Diamond. Pretend that you are now the owner of this diamond. Write a short story about what has happened in your life since buying this diamond.
Artist Vignette: Georges Braque
Georges Braque was a French painter known for his influence on the cubist style of art. He was born in 1882 near Paris, France, and like his father and grandfather, apprenticed as a house painter. However, by 1902 he decided to pursue the study of painting as a fine art. He emulated the style of other painters who used brilliant colors and a loose structure of forms to express themselves. He also, however, studied the work of Paul CÚzanne whose influence led him to paint in the manner that came to be called cubist. This technique involved straying from the traditional notions of realistic depictions of nature to create images inspired by geometric forms, such as cubes and rectangular prisms, as well as crystals. Cubist painters could see crystals in everything from the shape of a village on a hillside to the skin and features of a face.
Picasso, with whom Braque began to work closely in 1909, had been developing a similar approach to painting. Both artists produced paintings of neutralized color and complex patterns of faceted form, now called analytic cubism. Both artists also began to experiment with collage, a technique of constructing an image from the materials of everyday life, like newspapers, labels or pieces of fabric. His work with Picasso continued until Braque enlisted in the French army in 1914. Though he was severely wounded in World War I, Braque resumed his artistic career alone in 1917. At this time his work demonstrated a more personal style with brilliant colors and textured surfaces. He continued his artistic pursuits until his death in Paris in 1963, producing many paintings, graphics and sculptures.
Activity - Have students create a collage of shapes using various materials. Some students may wish to use crystals, like some cubists did, as the basis for their artwork.
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