Is there a size limit on diamonds in nature?

"Could one be dug up that is as big as a basketball? A car? A house? Bigger?"

Possibly, but due to their fragilic nature and the fact that they are generally forced up through the strata, they tend to get broken up long before they become accessable on the near surface.

There is not theoretical limit to the size of a diamond; but then diamonds are also known to break under pressure; so chances of finding one as big as a car are pretty much low. However, some really large diamonds have been discovered.

The size of diamond crystals varies between somewhat wide limits. The smallest sometimes measure less than a millimeter in diameter, but still smaller specimens (diamond sand) occur in nature. Small stones, measuring not more than one-quarter or one-third of a millimeter along the edge may be separated from a parcel of Brazilian diamonds by sifting with a sieve of fine mesh, the majority of these are octahedra, while cubes and rhombic dodecahedra are but rarely present. The faces of these very small crystals have the same surface characters as those of the larger crystals. By carefully washing for diamonds on the Cape diamond-fields, it is possible to obtain many stones very much smaller than those which usually come into the market, some indeed weighing no more than 1/32 carat. In the method of washing formerly practised at the Cape and also in Brazil, a large number of the smallest diamonds were lost, their value not being sufficient to justify a special collection of them, the improved washing machinery now in use is, however, capable of saving all the stones however small.

Stones of microscopic dimensions have only recently been observed, previous statements of supposed occurrences, such, for example, as their presence in the xanthophyllite of Zlatoust in the Urals, being based on errors of determination. Microscopic diamonds have been observed in large numbers in the diamond-bearing rock of the Cape, and there is no reason to doubt that they are present in other diamantiferous deposits. Smaller diamonds occur in larger number, larger stones are more limited in number, while very large specimens are so extremely rare and valuable that they are known by special and distinctive names, and in most cases form part of the crown jewels of various countries, these famous stones will be described further on in a special section.

The average size of diamonds found in different countries varies very considerably, formerly, when India and Brazil were the only localities at which diamonds were known to exist, stones exceeding twenty carats in weight were of great rarity. During the most productive period of the mines of Brazil, two or three years would elapse before a second stone of this size would be found, while very few stones exceeding one hundred carats in weight were ever found. The largest stone ever found in this locality, known as the "Star of the South", weighed in the rough 254.5 carats. The "Braganza", of the Portuguese crown, said to weigh 1680 carats, would rank as the largest diamond ever found in any locality were it indisputably a diamond, the probabilities are, however, that it is a fine piece of colorless topaz.

The chances of obtaining large diamonds in the Indian deposits were more favorable, a considerable number of diamonds exceeding one hundred carats in weight having been found there. Most of the large Indian diamonds are only known in their cut condition so that their original weight can only be estimated. Of large Indian diamonds, known in the rough condition in recent times, the "Regent" French crown jewels, is the heaviest, it weighed before cutting 410 carats, and produced a beautiful brilliant of 136 14/16 carats. Other large Indian stones will be described below in the section on famous diamonds, they are comparatively few in number. The heaviest of the large diamonds of ancient times is known as the "Great Mogul," which is said to have originally weighed 787.5 carats, there is no authentic information, however, either as to its weight or to its present whereabouts. The island of Borneo has produced one or two large stones, the largest reported diamond, weighing 367 carats, is, however, like the" Braganza," almost certainly not diamond, and probably nothing more valuable than a piece of rock-crystal.