Halo Cut (trademark). See polished
Halphen diamond. Streeter gives the only known record of this diamond: "Almost the only specimen of Red Diamond is a gem of a carat weight, bought by the author and sold to the late Mr. George Samuel for £800." Alternate name Halphen Red Diamond. Halphen Red Diamond. See halphen
hand loupe. See loupe Hanger Diamond. A 123-carat pale yellow rough diamond found in the early days of the South African diamond rush. It was reportedly purchased by Capt. E. S. Hanger of the Bloemfontein Rangers about 1868. Hanger sent the stone to Amsterdam to be cut into a brilliant rose-cut gem. It was subsequently purchased by the Countess of Char-lemont from County Tyrone, Ireland in 1870 for £300 and deposited in a bank as a future investment. No other details are available. Hannay Diamonds. See hannay, james
Hannay, James Ballantyne (1855-1931). A Scottish chemist who, in 1880, claimed to have produced minute diamonds by heating amorphous carbon with bone oi I and metallic lithium under great pressure. At the time, there was no satisfactory method for proving or disproving Hannay's claims. Later efforts to duplicate his experiments failed to pro-
duce diamonds. After World War II, a bottle labeled "Hannay's diamonds" was discovered in the British Museum of Natural History. Recent X-ray and cathodoluminescence tests have shown conclusively that the Hannay diamonds are all fragments of natural diamond. Since the Hannay diamonds are barely visible to the naked eye, it is believed that some accidental contamination of the starting materials occurred. See
hardebank. A harder-than-usual type of kimberlite, or blue ground. See
BLUE GROUND, KIMBERLITE, YELLOW GROUND.
Comparison of Mohs and the Knoop hardness scales.
hardness. The resistance of a substance to being scratched. Diamond is 10 on Mohs scale of hardness. Tests prove that diamond is approximately 10 to 150 times as hard as corundum, the next hardest mineral. The variation stems not only from differences obtained by different hardness-testing methods, but also from the fact that various directions on a given diamond's surface show a