DIAMOND IN BORNEO
HISTORICAL REVIEW of DIAMOND GEOLOGY and MINING
The diamond-fields of Borneo fall into two well-defined groups, one in the west of the island, in the district of the River Kapuas, the mouth of which lies a little below the town of Pontianak, the other in the south-east of the island, not far from the town Bandjarmassin, and nearly opposite the island of Laut (map). The three portions into which the western group may be divided are situated on as many different rivers, one being on the river Kapuas, a little below its confluence with the Sikajam, and the other two respectively on the rivers Landak and Sikajam, both tributaries of the Kapuas. The Landak deposits seem to have been known since the time the Malays settled in the island, and were mentioned by the Dutch mariners who first visited the coast; indeed, from the beginning the Dutch regarded the trade in diamonds in Borneo as their special monopoly.
In the west of the island diamonds occur in beds of alluvium, in masses of debris at the foot of mountains, and in the beds of streams and rivers flowing through diamantiferous districts. The alluvial deposits consist of gravel, sand, and more or less ferruginous clay, more rarely of conglomerate and sandstone. They are distinctly bedded, and vary in thickness from 2 to 12 meters, the diamonds being confined to the lowest bed, which consists of gravel.
These ancient gravels, which themselves show little or no signs of bedding, contain diamonds throughout their whole mass and are formed of more or less rounded rock-fragments. They are essentially river deposits, and occur in isolated patches of small area at the foot of the mountains or in the valleys, but always above the existing high-water level. The rock-fragments of which these gravels are composed differ widely in kind; white, yellow, or rose quartz predominates, but there are also present hard and compact gray and black quartzites, quartz-schists, clay-slates, quartz-sandstones, hornstones, hornblende, blue and violet corundum, and, in sparing amount, fragments of igneous rocks, so decomposed, however, that it is difficult to determine their original nature. In addition to these there are also to be seen scales of white mica, grains of magnetite, a few particles of cinnabar, and usually a little gold.
It is from these gravels that the diamonds now found in the beds of streams and rivers have been washed out. Both sedimentary and igneous rocks are found in situ in the neighborhood; among the former are clay-slates and quartz-schists with quartzites of Devonian age, conglomerates and clayey sandstones of much later date, probably belonging to the lowest Tertiary, that is, to the Eocene age. The igneous rocks include granite, diabase, gabbro, and andesite.
Diamonds are only found in places where the beds of Eocene conglomerate and clayey sandstone crop out at the surface. It has been thought by C. van Schelle, a mining engineer in Borneo that it is from these beds that the diamond has been derived. In any case the Devonian beds need not be considered, for no diamond has ever been found in alluvial debris derived from, or resting on, Devonian strata, in spite of the fact that such material has been carefully worked over for the gold it contains. The original mother-rock and the mode of origin of the diamond are therefore here as much a mystery as elsewhere, for no single crystal has ever been found in anything but what is obviously a secondary situation.
The working of the diamond-fields was in the hands of Chinese and Malays; the former work the deposits lying above high-water level, while the latter apply themselves to the alluvium in the present-day water-courses, extracting the diamantiferous gravel by excavating small deep pits reaching down to the solid rock, and washing the gravel in baskets. The methods in use in both cases are very primitive and inadequate, and no thorough investigation of the deposit has yet been made. 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 unpleasantly colored 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 cutting. Cubes are rare, but twinned crystals very frequent.
Borneo diamonds exhibit a fair range of color; the majority though colorless are disfigured by faults or blemishes of some kind or another. A few of the highly prized "blue-white" stones are found, and are of such singular beauty that their equal is nowhere to be found. After the colorless stones, those with a faint blue or yellow tinge are most abundant; more or less darkly colored stones (bort), as well as those of a gray color (carbonado), are fairly common. Stones in which a gray or black kernel is enclosed in a colorless and well-crystallized 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 color, quite distinct from carbonado, are occasionally found; when cut, such stones, though giving no play of prismatic color, display a magnificent luster, 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 were 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 diamond the size of a pigeon's egg, and weighing 367 carats; this stone will he again mentioned in the section devoted to large diamonds. The same prince was in possession also of two large stones, the "Segima" of 70 carats and another of 54 carats, both said to have been found in the island.
While in 1880, about forty Chinese worked the mines on the Sikajam River; 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.
Year Carats Value (florins)
1836 5473 110,601
It will be seen from the above table that the practice of recording the weight in carat of the imported diamonds ceased in 1844; moreover, the Customs Register, from which the above table has been compiled, was discontinued after 1848, so that there is no record of succeeding years. The number of stones imported into Java in each year, as set forth in the above table, represents very approximately the yearly production of Borneo, for it was at this period that the old Dutch East India Company was in its most flourishing condition, and the general prosperity created a demand for diamonds which drew almost the whole of the production of Borneo to Batavia; but all this ceased with the abolition of the company. In 1823 and 1831 the Dutch, seeing the demand for diamonds which existed in European markets, sought, unsuccessfully however, to increase the production by organizing systematic working of the deposits.
The merchants at Ngabang, the capital of Landak, have made a few estimates of the production of later times; they are as follows:
In the previous centuries the yield appears to have been much richer; while the deposits have been gradually exhausted, no new ones comparable in richness to the old have been discovered, and the abundance and comparative cheapness of Cape stones has rendered impracticable the exploitation of the poorer deposits. It is stated that in 1738 diamonds to the value of eight to twelve million Dutch florins were mined in Borneo, and even as late as the beginning of 19th century the value of the annual yield is said to have been as much as a million florins. The estimated annual yield at the present day it is supposed to be less than 5,000 carats.
The majority of the stones are roughly cut by the Malays in the island at Ngabang and Pontianak; there are diamond-cutting works also at Martapura, and the natives have been acquainted with the art of gem-cutting for centuries. At the present time scarcely any diamonds are exported, and it has even become customary to import Cape diamonds. The stones, which are yielded by the country, circulate almost exclusively in Oriental countries, very few finding their way to Europe.
Rafal Swiecki, geological engineer email contact
This document is in the public domain.