DIAMONDS.

Wanganui Chronicle, Volume XLIX, Issue 12632, 20 October 1905, Page 5

DIAMONDS.

When the members of the British Association reached Kimbeirley last month Sir William Croskes lectured'■appropriately on the diamond and its history. In South Africa, generally diamonds are found in " pipes " or shafts interrupting the country rock, which are filled with soft, yellowish material to the depth of 80ft. Below that the material is green or blue in colour. Many minerals are embeddded in the material, including diamonds, garnets, bfown mica, and ■iron ores such «6 usually form at high temperatures. Diamond is one form of crystalised cairbon, and it was at one time thought to have been produced in the pipe itself. It is, however, now generally admitted that the birthplace of the gem, as of most of the other liard minerals found with it., was elsewhere. As for the origin of diamonds, Sir William said that the process of manufacture "discovered by Professor Moissaa was suggestive. Pure iron and charcoal are melted togetbeer by the heat of the electric arc—a temperature about 4.ooodeg. Centigrade—and the liquid is suddenly plunged into cold water. The outer part contracts in becoming solid, so the inner cools under great pressure and the carbon crystallises i>n minute diamonds, whidh are obtained after dissolving the iron with acids, a long and tedious process; It is, therefore, possible that diamonds may be formed in molten iron far below the surface of the earth, and in some way broken out from the matrix. Diamonds, it seems, are often broken. The great CuHinan diamond, found in a mine not far from Pretoria, and" weighing almost 3026 carats, a little over four-thirds of a pound avoirdupois, is a fragment of a crystal which may have been twice the size. It also, like many large diamonds, shows by its .action on polarised light that it is in a state of strain, and evidently it will have to be very carefully handled.