To see a world in a grain of sand, And a heaven in a wild flower, Hold infinity in the palm of your hand, And eternity in an hour.
--William Blake, Auguries of Innocence
At first glance, sand is ubiquitous! It's found along river and stream banks, comprises dunes in arid regions, and forms beaches along the world's coasts. It also has many commercial applications--it? used in construction, ceramics, filtration systems, and abrasives.
When we look at sand, we typically think of it as a collection of homogeneous quartz grains. In reality, it's anything but uniform. Careful observation reveals the various rock materials from which it came, and the weathering, erosion, and transportation processes that produced this unique collection of granules.
Each sand sample holds the clues to a scientific mystery that can serve as the basis for inquiry investigations in Earth science, geology, or biology:
* What is the parent material for the sand?
* What tectonic forces emplaced the original rock and subsequently altered it?
* What happened to the rock--over thousands and millions of years--to produce the small pieces we collect today?
A classroom investigation of local sand samples reveals a fascinating Earth history that can address a variety of interdisciplinary scientific topics, provide rich inquiry experiences, and move beyond the science classroom to integrate history, culture, and art. This article describes these investigations in more detail.
The science of sand
Sand comes in many varieties--and each tells a story of weathering, transportation, and deposition that reflects a unique geographic and geologic location. Silica, especially in the form of quartz, is the most common constituent because of its hardness and stability. But sand can have other components, as well, such as small fragments of rocks or minerals, the remains of once-living organisms, and even small pieces of man-made objects!
What can a sand sample tell us? It reveals not only the rocks that provided the grains, but the weathering processes that acted upon them. For example, sand formed from granite initially contains an assortment of grains, including feldspars, quartz, and biotite (i.e., black mica). When subjected to chemical weathering, the less stable minerals decompose to form clay minerals. The presence of less stable minerals, such as feldspars and evaporites (e.g., gypsum), in a sand sample indicates less intense chemical weathering environments. The shape of the individual sand grains is another clue: Rounded particles indicate more intense weathering, and angular grains indicate less weathering and transportation.
The word sand refers to a size classification of sediments, which fall between larger, gravel-size particles and smaller, silt-size particles (see photo, p. 32). Sand typically has a diameter of between 0.0625 and 2 mm. The classic Wentworth Grade Scale (see "On the web") further divides sand into five subcategories that range from "very coarse" to "very fine." Diagrams, such as Folk's and Shepard's Classification Systems (see "On the web"), help researchers categorize sediments by their proportions of mud, sand, silt, and clay. A list of additional classroom sand resources is available online (see "On the web").
Using a microscope to see the individual particles that make up a sand sample is part of what makes this activity so engaging for students--they never fail to appreciate the "wow!" factor.
Local sand history
Whether from beaches, river sandbars, desert dunes, or glacial moraines, natural sand deposits are available to most classrooms. Our initial sand investigation is usually a local one: Students collect naturally deposited sand and then conduct a regional, in-depth investigation of its "Earth journey" through mineralogy, weathering, and transportation processes. …