Hoyt Belknap, age 14, of Haggerstown, Md., for his question:

WHAT IS BASALT?

Basalt is a heavy, hard, dark colored rock made of tiny mineral grains. Basalt is crystallized lava which once poured red hot from volcanoes.

The grains of basalt are crystals, made chiefly of two minerals: plagioclase and pyroxene. Sometimes the rocks have small cavities filled with such minerals as calcite.

Sometimes, when lava cools to form basalt, it splits into four , five  or six sided columns. Cliffs consisting of basalt columns are famous tourist sights in many parts of the world.

The Palisades along the Hudson River, which consist of a variety of basalt called diabase, and the cliffs along the Columbia River in Washington are well known examples of such columnar basalt sheets.

The Devils Postpile National Monument in the Sierra National Forest of California is a spectacular mass of blue gray basalt columns. The columns resemble a pile of posts and tower 60 feet above the San Joaquin River.

Basalt is used in road making and construction.