Editing Diamond (section)

==== Hardness ====
[[File:Vickers anvil diamons.jpg|thumb|The extreme hardness of diamond in certain orientations makes it useful in materials science, as in this pyramidal diamond embedded in the working surface of a [[Vickers hardness test]]er.]]
Diamond is the hardest material on the [[qualitative property|qualitative]] [[Mohs scale of mineral hardness|Mohs scale]]. To conduct the [[unit of measurement|quantitative]] [[Vickers hardness test]], samples of materials are struck with a pyramid of standardized dimensions using a known force – a diamond crystal is used for the pyramid to permit a wide range of materials to be tested. From the size of the resulting indentation, a Vickers hardness value for the material can be determined. Diamond's great hardness relative to other materials has been known since antiquity, and is the source of its name. This does not mean that it is infinitely hard, indestructible, or unscratchable.<ref>{{Cite web|date=December 16, 2015|title=Diamonds Are Indestructible, Right?|url=https://dominionjewelers.com/diamonds-are-indestructible-right/|access-date=October 31, 2020|website=Dominion Jewelers|language=en-US|archive-date=September 26, 2020|archive-url=https://web.archive.org/web/20200926001227/https://dominionjewelers.com/diamonds-are-indestructible-right/|url-status=live}}</ref> Indeed, diamonds can be scratched by other diamonds<ref>{{cite journal|vauthors=Seal M |title=The abrasion of diamond |journal=Proceedings of the Royal Society A |volume=248 |issue=1254 |date=November 25, 1958 |pages=379–393 |doi=10.1098/rspa.1958.0250|bibcode=1958RSPSA.248..379S }}</ref> and worn down over time even by softer materials, such as vinyl [[phonograph record]]s.<ref>{{cite web |vauthors=Weiler HD |title=The wear and care of records and styli |orig-date=1954 |date=April 13, 2021 |via=Shure Applications Engineering |url=https://service.shure.com/s/article/stylus-wear-and-record-wear?language=en_US |access-date=August 25, 2024 |archive-date=March 26, 2023 |archive-url=https://web.archive.org/web/20230326031532/https://service.shure.com/s/article/stylus-wear-and-record-wear?language=en_US |url-status=live }}</ref>

Diamond hardness depends on its purity, crystalline perfection, and orientation: hardness is higher for flawless, pure crystals oriented to the [[Miller index#Case of cubic structures|<111>]] direction (along the longest diagonal of the cubic diamond lattice).<ref>{{cite book|pages=142–147|url=https://books.google.com/books?id=jtC1mUFZfQcC&pg=PA143|title=Properties, Growth and Applications of Diamond|vauthors=Neves AJ, Nazaré MH|publisher=[[Institution of Engineering and Technology]]|year=2001|isbn=978-0-85296-785-0|access-date=November 9, 2020|archive-date=February 19, 2023|archive-url=https://web.archive.org/web/20230219072829/https://books.google.com/books?id=jtC1mUFZfQcC&pg=PA143|url-status=live}}</ref> Therefore, whereas it might be possible to scratch some diamonds with other materials, such as [[boron nitride]], the hardest diamonds can only be scratched by other diamonds and [[Aggregated diamond nanorod|nanocrystalline diamond aggregates]].

The hardness of diamond contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in [[engagement ring|engagement]] or [[wedding ring]]s, which are often worn every day.

The hardest natural diamonds mostly originate from the [[Copeton Dam|Copeton]] and [[Bingara]] fields located in the [[New England (Australia)|New England]] area in [[New South Wales]], Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is associated with the [[crystal growth]] form, which is single-stage crystal growth. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.<ref>{{cite magazine|vauthors=Boser U|title=Diamonds on Demand|url=http://www.smithsonianmag.com/science-nature/diamonds-on-demand.html|magazine=[[Smithsonian (magazine)|Smithsonian]]|volume=39|issue=3|pages=52–59|year=2008|access-date=June 13, 2009|archive-date=March 2, 2012|archive-url=https://web.archive.org/web/20120302163915/http://www.smithsonianmag.com/science-nature/diamonds-on-demand.html|url-status=dead}}</ref>

Diamonds cut glass, but this does not positively identify a diamond because other materials, such as quartz, also lie above glass on the [[Mohs scale]] and can also cut it. Diamonds can scratch other diamonds, but this can result in damage to one or both stones. Hardness tests are infrequently used in practical gemology because of their potentially destructive nature.<ref name=read/> The extreme hardness and high value of diamond means that gems are typically polished slowly, using painstaking traditional techniques and greater attention to detail than is the case with most other gemstones;<ref name="hazen">{{cite book|url=https://books.google.com/books?id=fNJQok6N9_MC&pg=PA7|pages=7–10|title=The diamond makers| vauthors = Hazen RM |publisher=Cambridge University Press|year=1999|isbn=978-0-521-65474-6}}</ref> these tend to result in extremely flat, highly polished facets with exceptionally sharp facet edges. Diamonds also possess an extremely high refractive index and fairly high dispersion. Taken together, these factors affect the overall appearance of a polished diamond and most [[diamantaire]]s still rely upon skilled use of a [[loupe]] (magnifying glass) to identify diamonds "by eye".<ref>{{cite book|url=https://books.google.com/books?id=Jm3FwBiHaI4C&pg=PA37|pages=34–37|title=Synthetic, Imitation and Treated Gemstones| vauthors = O'Donoghue M |publisher=Gulf Professional |year= 1997|isbn=978-0-7506-3173-0}}</ref>