Melissa Thompson, age 12, of Hot Springs, Ark., for her question:

WHAT IS NOVACULITE?

Novaculite is a fine grained variety of quartz that at one time was used for grinding stones. It is an extremely hard rock and one that is probably sedimentary, meaning that its organic matter was probably deposited many centuries ago by water or ice. The rock is composed essentially of microcrystalline quartz.

A novaculite grinding stone is also called a whetstone. Its uniform hard grains make it capable of grinding quickly and withstanding wear.

A whetstone, actually, is any abrasive stone, natural or artificial, that is used for grinding and sharpening. At the present time, artificial abrasives such as silicon carbide and aluminum oxide are most often used.