CTS Guide: Earth’s Materials and Systems, pp 205-205- Section IV Research Summaries

Rocks and Rock Particles

  • Children often fail to recognize that words like boulder, gravel, sand, and clay have specific meanings related to the average size of fragments. For example, children think of clay as being sticky, orange stuff found underground rather than as a veryfine particle of rock (Driver et al. 1994).

  • Freyberg (1985) found that the word rock is used in many different ways in our common language, contributing to the confusion over what a rock is geologically. Many students think rocks have particular size, not too large and not too small, rather than being characterized by what they are made of.

  • Some students use “heaviness” to describe rocks. When students were shown different types of rocks and asked whether they were rocks, several students thought pumice was too light to be a rock (Osborne and Freyberg 1985).

  • Happs (1982) found students tend to use different meanings for rock fragments than scientists, who classify the fragments by average size. They have difficulty with the idea of rock types being a range of sizes. They use words such as boulder, gravel, sand, and clay in ways related to where they are found, rather than seeing them as rocks of different sizes. For example, they say that boulders are larger than rocks and have rolled down a slope, gravel is something on the side of roads, sand is on beaches and in the desert, and clay is red and underground. Sand is defined as coming from a beach or desert rather than being a particle of a certain average size. Younger students often identify rocks by their weight, hardness, color, and jaggedness. Therefore, some students believe that rocks are larger, heavier, and more jagged than stones.

  • In studies by Happs (1982, 1985), students had difficulty making the distinction between “natural” things and those created or altered by humans. For example, some students considered brick a rock because part of it comes from natural material. Conversely, some students thought cut, smooth, polished marble was not a rock because humans made it smooth and so it was no longer natural.