It is the purpose of this unit to acquaint the student with the intriguing world of crystals, their structure, formation, and uses.
Most students when confronted with a well-formed quartz crystal, or a purple fluorite, or a polished geode, literally jump about demanding to know “Who made this?” and “How did they make this?”. And the subject of diamonds and other gems is avariciously attended to with wide eyes and listening ears. Since the actual atomic structure can be drawn and modeled in a wide variety of mediums even the more humdrum aspects can be made inviting. And the chemical concoctions that can result in some homemade crystals bring out the white-coat scientist in even the most reluctant student. Many of the students own small personal calculators that are solar-powered, or have seen the advertisements in discount store circulars for solar powered exterior lighting. These objects provide a good jump-off point for discussions about crystals and technology.
My unit on crystals will be divided into three categories covering three areas of study. The first area will deal with the actual structure of crystals beginning with a look at the atom, some simple atomic drawings (Bohr models) of elements, and a study of the periodic table of the elements. Next we will look at compounds and their bonds. This will lead to the understanding of how crystals “look” and the shapes they can take. Within this section we will draw and construct in three dimensions paper models of six of the basic crystal shapes. We will also grow some of our own crystals in the laboratory.
The second major heading in my unit will focus on minerals. We will learn about the characteristics of a mineral: the chemical composition, mineral color, luster, cleavage, hardness (and how this property is related to crystal structure), and specific gravity. The characteristics of minerals lend themselves nicely to a mineral identification lab., and a lab. on specific gravity of minerals and selected rock samples. Some of the other topics in this section will include a study of the various forms of quartz; gems, especially diamonds; the formation of mineral crystals—by igneous, sedimentary, and metamorphic processes; and some stories of famous (or infamous) gems.
The final section of this unit will delve into the uses for crystals which modern technology has fostered, specifically solar cells, transistors, and liquid crystals.
The unit is designed for the middle school age level, specifically for the eighth grade Earth Science curriculum. In the two years that I have used this curriculum unit with my eighth grade classes I have amplified or omitted sections depending on the interest and abilities of the various classes. In this way I have been able to use the unit with students that range in ability from very high to very low.
Throughout this paper I am indebted to the teaching and guidance of Dr. Werner Wolf and to the following books and sources:
On the topic of crystal growth and structure: Alan Holden and Phylis Morrison, Crystals and Crystal Growing; and Elizabeth Woods, Crystals—A Handbook for School Teachers.
On the topic of quartz and related minerals: Cornelius Hurlbut, Minerals and Man.
On the topic of gemstones, natural and man made: Cornelius Hurlbut, Minerals and Man; Joel Arem, Man-made Crystals; and Paul O’Neil, Gemstones.
On the topic of liquid crystals: Frederick Kahn in Physics Today; and Glenn Brown and Peter Crocker in C&EN.
On the topic of solar cells and semi-conductors: Bruce Chalmers in Scientific American; and Christopher Swan, Suncell; Energy, Economy, and Photovoltaics.