Let's get out our notebooks again and write descriptions of a variety of rocks. We'll just make notes on the physical characteristics, such as color and composition.

a. Color.

The colors of opaque rocks are best observed when the rock is scratched across a piece of unglazed tile. (Note: The streak that is left by the rock may be different from the rock's color.)

Now, excuse me, brilliant scientist, but how can we "best" observe the colors of opaque rocks by scratching them across a piece of unglazed tile, if the streak that is left by the rock is different from the rock's color? That is exactly what the brilliant scientist's notes said, and it makes no sense at all. What do I know? I'm just a writer.

Our resident geologist agrees; however, he would change the statement to say that rocks sometimes APPEAR to be of different colors than the streaks they leave. The rocks appear to be darker than the streaks, but usually the streaks are of the correct colors.

Back to the brilliant scientist's notes:

Transparent and translucent rocks can be tested for their color or lack of color. Sort the rocks on the basis of color or number of different colors.

b. Composition.

Study the surface of the rocks with a hand lens, and note whether they are made of one, or more than one, kind of material.

Sort the rocks by the size of the particles they contain and by whether or not the particles are crystalline.

Break a rock (cover it with a cloth or bag before you hit it with the rock hammer), then compare the inside of the rock with its outside features. (Wear goggles.)

In breaking rocks, you may find that some break in certain ways (along cleavages). That is really called "fracturing." Note the directions of the fractures (e.g., the number of parallel lines or faces).