Kathy Gilberts age 10, of Pasadena, Texas; or her question:

What exactly is the lead in a pencil?

The so called lead in a pencil is graphite, This soft and oily, grey black mineral is related to shiny black coal, which is not hard to believe: It is also related to the clear, sparkling diamond. As a chemical, graphite is more closely akin to the diamond, for both are forms of pure carbon. In its history, graphite is more closely akin to coal. The story of the so called lead in a pencil may have started almost 300 million years ago.

It began as our coal beds began,, in a strange and ancient forest rooted in a stagnant swamp. There were tree ferns, lavish mosses and giant horsetails. Huge amphibians wallowed in the mud and gauzy insects zoomed through the air. This was the Carboniferous Period of earth s history. The strange forests of this period provided the carbon for our coal and graphite,

The logs and fallen foliage of a forest usually decay. This debris is attacked by tiny bacteria which break it up into simple chemicals. These chemicals provide the nourishment for new generations of plants. The new generations will in time decay to feed still newer generations. This decay cycle did not happen in the ancient swamp forests. For the stagnant waters were without oxygen and decay bacteria must have oxygen to survive. Debris from the carboniferous forests fell into the stagnant water and collected in soggy layers and huge piles.

In time the swamps drained and the swamp vegetation was buried under deeper and deeper layers of earth and rocks. Plant material is mostly carbon, cementing materials and water. Under heat and pressure, the moisture and lighter materials escaped or were driven out of the buried debris,

After millions of years, it became a bed of lignite, a low grade brown coal which is about 65% carbon. With more time, more heat and more pressure it became glassy black bituminous coal which is about 88% carbon. In some regions, bituminous coal became hard anthracite which is 90% carbon. Through the ages, the coal became a better and better fuel.

The carbonizing process does not stop with hard anthracite coal. With more time and pressure, the bed of ancient debris becomes graphite. It is now no use as a fuel for graphite can withstand terrific heat, Has the buried treasure now lost its value? Not at all. Graphite still has a job to do in foundries and furnaces, though not as a fuel. It is used to line molds to hold molten metals„

In graphite, the carbon is in small crystals which tend to rub off on a rough surface. This feature makes it useful as a writing material. The small carbon crystals make graphite smooth and slippery to the touch. Mixed with grease it is used to lubricate machinery. Powdered graphite is used in certain paints. These jobs are far from the ancient swamp forests where the graphite began its story.