Mining the Carbonado

Hawera Star, Volume L, 20 December 1930, Page 18

Mining the Carbonado

Q’NIOJD thrown away av* useless, ami later sol’d at Is a carat, these huge, hard rough diamonds bow bring as high as £3<7 a carat iir the invarket. Of no value as gems, they exceed the i.vhito diamonds in toughness), ami are the best material for use in- the diamond drill. 'The carbonado, which is the Brazilian' name, is called: “Brazil’s naltural mono ply' ’ bv W. N. IP. Reed, assistant editor of “The Engineering awl Mining Journal,” (New York). In an illustrated descriptive article in his paper lie says:

“Africa; is by far the greatest producer of white diamonds, but, in the opinion cf some experts, ©rizal leads the*, world) in the production of white stones of the most perfect brilliance. “The last named country enjoys the distinction of .possessing- the* only' known commercial deposit's of the carbonado, a so-called l anthracite variety of diamond, 'dark gray' to black in shade.

“Three varieties of 'diamonds are known: the crystalline gem stone; the bort, frequently' translucent, and resenabling the carbonado, in structure; and the true carbonado.

■“Until invention of the diamomldrill, carbonados were of little value, hut so rapidly has a use for them developed that deep exploration of drills would in present- practice be impracticable without them. Prosjpecting bv the use of the diamond-driM is now approved by engineering everywhere.

A Monster of 3,000 Carats

Valuable for Drill Work

j Carbonados, have no cleavage, and -are j thus much better than rrystilline diamonds for use in drills. In tact, the carbonado possesses the distinction of being the toughest substance on earth. ‘The largest diamond ever tfound was a carbonado. Tt was discovered in the State of Bahia, Brazil, in 11895. 'The stone weighed 307 S carats, and was ! worth' at the present market more than | £60,000. This cai'bon broken into sizes suitable for use in diamond-drills, j rendered great service in ithe ox:plora- ; tion of the Alesabi Range. ‘Beside this giant stone- the 'Great Mogul and the Kelt in-on r rate low in the s-cale, as to the size, among the famous m-ond-s of history'. ‘‘Although diamonds of the 'crystalline variety' were mined in Brazil as early' as 1725, only since IS7O h-ave carbonados been known in that great country'. At that time the carbons were discarded as waste materials.

“The carbonados range from minute fragments up to several hundred carats. About 98 per cent, of the product is used in drillsi, the remainder, in the form of powder, being used as a polish-, ing material in the cutting of white diamonds, -and for abrasive purposes.

“In a technical, sense, railbomwlop are not ‘drest.’ Stones, of larger than commercial- size are split- and broken under pressure b.v a sharp wedge of siiper-h'..rdenr'.l stool of German manufacture.

“In 1024. Arthur S. Bandin', of New York, an importer of industrial diamonds, went to Bahia., to investigate the possihitries of mining carbonados on a targe scale by modern mechanical methods.

I “ ‘Prior to 1570.’ said 1 Mr. Brandler, j rough diamonds in Amsterdam, one of .the Bahia correspondents of the dia;mond merchants sent over some black stones front Bahia which he thought had diamond indications. Among these was a large black stone, of some 2000 carats, used as a counterweight on a door. “ ‘One of the diamond-workers having difficulty in polishing the facets of a white diamond, said., one day. to a follow-workman: “I am going to try a piece o? this big black stone." “ ‘He split off a corner, powdered it, and found that it was better than white diamond powder Now the stones are] j used to extract cores as small as a! I broom-handti'C or as large as a marble* ! column. Perhaps as 'many dramondj drills are now in operation in New | York city as in any mining region' in j the world.’, ’ I Black diamonds occur mixed with .\ ash -and gravel, and are hard to iden- • tifv. As the deposit containing the j stones consist of loose gravel on a limestone bedrock, with I's to 20 feet, of | pure wind over it, the problem of mining is divided' into two phases: the removal of the sand, andi the later separation of the sand' and carbon-bearing gravel.