Kathryn Geib, age 13, of Kalispell, Mont., for her question:

WHAT ARE BASALT COLUMNS?

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

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 columnar basalt sheets.

Other famous basalt columns include the Devil's Postpile, south of Yosemite National Park in California, and Giant's Causeway in Ireland.

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

Basalt is used for making roads and as a building stone. It makes up most of the Atlantic and Pacific volcanic islands.