Kathy Williams, age 10, of Cleveland, Oklahoma, for her question:

What are gneiss rocks?

Some rocks are so hard that they strike sparks when you bash them together. Ages ago, our ancestors used them instead of matches. Their word for these sparky stones was something like our word "gneiss," When we say it, we ignore the first letter and the rest of the word sounds like "nice." Our gneiss rocks may be hard enough to strike sparks. But our ancestors who named them did not know a gneiss rock has suffered through ages of bashing and fiery heat inside the earth.

Good places to find gneiss rocks are in the mountains and around Lake Superior. If your hobby is rocky minerals, you are almost sure to have a few gneiss samples in your collection. True, they cannot compare with the handsome, smooth and colorful minerals. But their looks tell a fascinating story. You might say that they look like rough and ready everyday rocks, very hard and sturdy. They are bumpy stones made from various ingredients that add their own rather drab colors. Some gneiss samples are tinged with red, grey or green, and others are nearly white or nearly black,

The blotchy colors are speckled and freckled all over the rough, bumpy rock. But if you look closely, you see that they are arranged in bands, somewhat like rocky pages pressed and glued tightly together. This gives a striped, banded look. If you bash the rock hard enough with a hammer, chances are it will break apart at the banded seams. This suggests that the mineral was crushed flat under tremendous pressure in the earth.

But there is far more to the story of how the earth formed these sturdy rocks. The original ingredients were quartz and feldspar, plus maybe horblende,~ mica or other minerals. Some of the ingredients may have been slates and clays that sifted to the bottom of muddy lakes. Others were melted deep underground and erupted by volcanos. When the hot lava cooled, they became solid. Most of these minerals stay more or less as they are, buried underground or gradually wearing away on the surface.

But the ingredients for making gneiss rocks were not allowed to rest in peace. They were bashed and battered, crushed and pressed together in multiple sandwiches. These adventures were so tough on them that they actually changed into different

What are gneiss   for Thursday, November 4, 1971 minerals. Several other minerals also become completely changed by heat and pressure, deep in the earth's crust. We call them metamorphic rocks. Limestones and sandstones that form muddy sediments in the water are sedimentary rocks. The lavas created by fiery volcanoes are igneous rocks.

The banded stripes of a gneiss sample may tell a few things about its history. Embedded pieces that look like glassy lenses mean that bits of mica were pressed into the sandwich. Flattened pebbles show that the pressure stopped before they were crushed completely flat. Dark, flaky layers may mean that hot lava oozed into the rocky sandwich before it was finished.