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'Antennas' give opponent bad reception; Diamonds cut diamonds.

Q: What is the purpose of the antennas on the giraffe's head? (Don, Houston, Texas)

A: The horns do look a little like rabbit-ear antennas but their purpose is obscure. The females don’t use their lighter ones at all. The males use theirs incidentally in a fight. The scarred and battered big horns on a male (called ossicones, meaning "hair-covered horns") receive and occasionally deliver blows. A bull’s primary weapons, however, are two smaller horns in back of and below the big horns. Using these and his entire massive head, he clubs the other guy into submission to win reproductive rights.

A young bull showing his back fighting horns. The top bird in the photo is sitting beside one of the back horns. The redbilled oxpecker keeps ticks and other vermin from the skin. [© Spook Skeleton, Nature-Wildlife, used with permission]

The African sun beats down. A lanky stranger strolls close to the old bull. The challenger raises his horned head, faces the other bull, and stands erect, stiff legged.

The old bull responds in kind. The duel is on. They entwine necks and lean on each other to measure weight and strength. Preliminaries over, each giraffe braces himself by spreading his forelegs.

The young one strikes the first blow. Typically, a fighting bull draws his head and neck "sideways and swings upward and backward over his shoulder" to strike his opponent with his back horns, thereby "concentrating the blow in a small area," writes Richard Estes in The Behavioral Guide to African Mammals.

Four young bulls, engaged in mock battles. Note the "necking." [© Spook Skeleton, Nature-Wildlife, used with permission]

The old bull skillfully rocks, lessening the terrible blow, and swings his own head — a mass of piled bone twice the weight of his opponent’s. (Bulls layer bone over the entire skull surface year after year from age four on.) Wham! He connects; the stranger falls, knocked unconscious. (Usually, however, the loser simply gives up, lowers his head and ears, tucks in his chin, and slinks away.)

The old, top-male bull walks away with the cow.

Further Reading:

Nature - Wildlife, The photography and behavior of the giraffe by Spook Skeleton

Richard D. Estes, The Safari Companion , White River Junction, Vermont: Chelsea Green Publishing Company, 1999.

Q: If no substance is harder than a diamond and no other material can scratch a diamond then how do they cut a diamond for jewelry? (Bob, York, Pennsylvania)

A: Basically, diamonds cut diamonds. We can also trick a diamond by taking advantage of its weaknesses.

In the late fifteenth century, a craftsman cut diamonds by placing a chisel at a weak spot in the diamond’s crystal structure and then whacked the chisel with a mallet. If he had selected well, the diamond neatly fell in two. If he picked the wrong spot, the diamond shattered.

A diamond crystal is essentially two pyramids stuck together — an octahedron. See figure. Consequently, the craftsman can cleave the crystal in any one of the four directions parallel to the crystal faces and, theoretically, succeed.

Diamond in the rough and octahedron. A diamond crystal is essentially two pyramids stuck together — an octahedron. [USGS]

We still cleave diamonds, especially big ones, into suitable pieces before sawing. Diamond saws were invented in the twentieth century. This was a major innovation because it permits cuts against the grain of the diamond without shattering.

The saw rotates at about 4,000 revolutions a minute and cuts with diamond dust. The rim of the paper-thin disc (originally made of steel and now of phosphor bronze) is saturated with diamond dust and lubricated continually with oil. The diamond dust sticks to the oiled rim. As the dust on the rim cuts, diamond dust whirs away from the cutting blade and continually replenishes rim dust. It takes time (about four to eight hours for a 1-carat rough diamond) but gradually diamond dust cuts the diamond crystal.

Further Reading:

he Rise and Fall of Diamonds by Edward Jay Epstein

Diamond Cutters International, The Diamond Guy:

Diamonds — getting into shape by Fred Cuellar

(Answered June 17, 2005)