Even with the dramatic growth in synthetic diamond, the demand by industry for natural diamond has not declined. If anything, the real cost of natural diamond has actually increased especially for higher quality stones. The demand for diamonds for jewelry is such that premium stones used in the 1950s for single-point diamonds are now more likely to be used in engagement rings; while very small gem quality stones once considered too small for jewelry and used in profiling dressing discs, are now being cut and lapped in countries such as India. With this type of economic pressure it is not surprising that the diamonds used by industry are those rejected by the gem trade because of color, shape, size, crystal defects such as twins or naats, or excessive inclusion levels; or are the processed fragments from, for example, cleaving gems. Although significant quantities of processed material are still used in grinding wheel applications, it is the larger stones used in single-point and form-roll dressing tools that are of most significance. Here the quality of the end product depends on the reliability of the diamond source and of the ability of the tool maker to sort diamonds according to requirements. The highest quality stones will be virgin as-mined material. Lower quality stones may have been processed by crushing and/or ball-milling, or even reclaimed from old form dressing rolls or drill bits where they had previously been subjected to high temperatures or severe conditions.
5.6.13 Forms of Natural Diamond
Natural diamond grows predominantly as the octahedral form that provides several sharp points optimal for single-point diamond tools. It also occurs in a long-stone form, created by the partial dissolution of the octahedral form as it ascended to the Earth’s surface. These are used in dressing tools such as the Fliesen blade developed by Ernst Winter & Son. It should be noted, though, that long-stone shapes are also produced by crushing and ball-milling of diamond fragments; these will have introduced flaws which significantly reduce strength and life. The old adage of “you get what you pay for” is very pertinent in the diamond tool business!
Twinned diamond stones called maacles also occur regularly in nature. These are typically triangular in shape. The twinned zone down the center of the triangle is the most wear-resistant surface known and maacles are used both in dressing chisels as well as reinforcements in the most demanding form-roll applications.