Distribute a tray of materials to each group, but hold back the quartz for now. Write the names of the four rocks on the class chart and pronounce them for the class:

Sandstone … Granite … Conglomerate … Basalt.

Allow a few minutes for students to pass the rocks around and identify each one, then ask students to hold on to whichever rock they have.

Now issue a challenge:

• You have a rock. You have a magnifying glass. You have your senses. Use all your powers of observation to learn everything you can about the rock you are holding.
• List at least six observations about your rock. Write your observations in your notebook. Include some drawings, too.

Have the students work in pairs. Though each student will describe only one rock, comparing the two rocks might elicit more observations.

As you circulate among the groups, draw attention to the different materials the rock is made of.

• Are you talking about the black, bumpy stuff or the white, shiny stuff?
• Is the rock made of the same stuff all the way through?

Make sure students are recording their observations in their notebooks [Observations of a rock], and that they are distinguishing their "data" from their "ideas about data."

As the students finish up their observations, recall the investigation question:

What have we learned about rocks so far, just by observing them carefully?