DIAMOND: OCCURRENCE IN BORNEO 219 



methods in use in both cases are \ ery primitive and inadequate, and no thorough investigation 

 of the deposit has yet been made. An improvement in the system might probably be easily 

 made if the diamond-seekers, who are for obvious reasons very uncommunicative, could be 

 persuaded to volunteer the necessary information. 



The diamonds of Borneo are, on the average, of poor quality ; the proportion of faulty 

 and unpleasingly coloured stones being sometimes stated to be greater here than in Brazil. 

 The diamonds are almost invariably either more or less water-worn or fragmentary and 

 irregular. The predominating crystalline forms are the octahedron and the rhombic 

 dodecahedron ; regular octahedra, which are not infrequent, are known to the Malays as 

 " perfect stones," since according to their ideas such stones require little or no cuttmg. 

 Cubes are rare, but twinned crystals very frequent. 



Borneo diamonds exhibit a fair range of colour ; the majority though colourless are 

 disfigured by faults or blemishes of some kind or another. A few of the highly prii^ed 

 " blue-white " stones are found, and are of such singular beauty that their equal is 

 nowhere to be found. After the colourless stones, those with a faint blue or yellow 

 tinge are most abundant ; more or less darkly coloured stones (bort), as well as those of a 

 grey colour (carbonado), are fairly common. Stones in which a grey or black kernel is 

 enclosed in a colourless and well-crystallised shell are sometimes met with ; such a stone is 

 known to the Malays as "soul of the diamond," and is considered to augur a poor deposit. 

 Although the stone itself is regarded as a talisman, and worn round the neck in the belief 

 that it will bring luck to its owner, yet at the spot at which it was found work is immediately 

 abandoned and a fresh place chosen. On the other hand, the presence of the blue corundum 

 is considered to be a good sign by the diamond seekers. Diamond crystals of a deep, black 

 colour, quite distinct from carbonado, are occasionally found ; when cut, such stones, though 

 giving no play of prismatic colour, display a magnificent lustre, and are in great request for 

 use in mourning jewellery. 



With regard to the size of stones from this locality, it may be asserted that 95 per 

 cent, of the whole output is constituted by stones which weigh less than 1 carat. Next 

 in abundance come stones between 1 and 5 carats in size, while those exceeding this size 

 are very rare. Several diamonds of large size were found in the district belonging to the 

 Malay Prince of Landak, and are now in his possession ; owing to their massive silver 

 setting they cannot be weighed, but several have been estimated by C. van Schelle at over 

 100 carats. In the possession of the Rajah of Mattan is a supposed diamond the size of a 

 pigeon's egg, and weighing 367 carats ; this stone, which is probably only rock-crystal, will 

 be again mentioned in the section devoted to large diamonds. The same prince is in 

 possession also of two large and undoubtedly genuine stones, the "Segima" of 70 carats 

 and another of 54 carats, both said to have been found in the island. 



While in 1880 the mines on the Sikajam river were worked by about forty Chinese 

 only, those in Landak gave employment to about 350 workers. The alluvial deposits on 

 the Kapuas river are no longer systematically worked ; single pits may be sunk here and 

 there, but the production is quite insignificant. 



The diamond-bearing deposits in the south of the island, namely, in the districts of 

 Tanah-Laut, Martapura, and Riain are of recent formation, and overlie Eocene strata in 

 the same way as those described above. These Tertiary strata, which in places include thin 

 beds of coal, rest on ancient crystalline rocks, such as mica-schist, chlorite-schist, talc-schist, 

 and hornblende-schist, and like these are inclined and faulted. Interbedded with the 

 Tertiary strata, and specially towards their base, are sheets of recent eruptive rocks 

 (andcsites). The diamond-bearing deposits form a broad band round the seaward slopes of 



