Heather Jenkins, age 13, of Grand Forks, N.D., for her question:

WHAT IS LAPIS LAZULI?

Lapis lazuli is a blue rock that has been used since ancient times for ornamental purposes. It consists essentially of the blue mineral lazulite and contains a small amount of calcite, pyroxene and other silicates.

Lapis lazuli has been used since olden days for mosaics and other inlaid work, carved ornaments, vases and other objects. It is also cut cabochon as a gem. Cabochon means the gem is cut into an oval or convex hemispherical form, polished but not cut into facets.

Lapis lazuli was formerly ground and used as pigment called ultramarine but has been replaced by artificial ultramarine. An imitation of lapis lazuli, obtained by straining cracked quarts, is known as Swiss lapis.

The mineral jasper, when stained blue, is called German lapis or blue onyx.

Lazurite is essentially a sodium aluminum sulfosilicate. It varies in color from deep azure blue to greenish blue, is translucent and has vitreous luster.