Editing Diamond (section)

=== Mechanical ===
==== 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>

==== Toughness ====
Somewhat related to hardness is another mechanical property ''toughness'', which is a material's ability to resist breakage from forceful impact. The [[toughness]] of natural diamond has been measured as 50–65&nbsp;[[Megapascal|MPa]]·m<sup>1/2</sup>.{{contradiction inline|reason=Unit of toughness as given at the article on toughness is newton-metres per cubic metre, dimensionally equivalent to newtons per square metre i.e. pascals. What is this factor of m^{1/2} doing here? Should we actually be talking about and linking to [[Fracture toughness]] (which unfortunately doesn't have a discussion of units)?|date=October 2023}}<ref>{{cite book| vauthors = Lee J, Novikov NV |title=Innovative superhard materials and sustainable coatings for advanced manufacturing|url=https://books.google.com/books?id=EXGcDYj8HvEC&pg=PA102|page=102|publisher=Springer|year=2005|isbn=978-0-8493-3512-9}}</ref><ref>{{cite book| vauthors = Marinescu ID, Tönshoff HK, Inasaki I |title=Handbook of ceramic grinding and polishing|url=https://books.google.com/books?id=QCvqtRJJ4XwC&pg=PA21|page=21|publisher=William Andrew|year=2000|isbn=978-0-8155-1424-4}}</ref> This value is good compared to other ceramic materials, but poor compared to most engineering materials such as engineering alloys, which typically exhibit toughness over 80{{nbsp}}MPa·m<sup>1/2</sup>. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a [[cleavage plane]] and is therefore more fragile in some orientations than others. [[Diamond cutting|Diamond cutters]] use this attribute to cleave some stones before faceting them.<ref name=harlow/> "Impact toughness" is one of the main indexes to measure the quality of synthetic industrial diamonds.

==== Yield strength ====
Diamond has compressive yield strength of 130–140{{nbsp}}GPa.<ref>{{cite journal | vauthors = Eremets MI, Trojan IA, Gwaze P, Huth J, Boehler R, Blank VD |title=The strength of diamond |journal=Applied Physics Letters |date=October 3, 2005 |volume=87 |issue=14 |pages=141902 |doi=10.1063/1.2061853|bibcode=2005ApPhL..87n1902E}}</ref> This exceptionally high value, along with the hardness and transparency of diamond, are the reasons that [[diamond anvil]] cells are the main tool for high pressure experiments.<ref name=Dubrovinsky>{{cite journal | vauthors = Dubrovinsky L, Dubrovinskaia N, Prakapenka VB, Abakumov AM | title = Implementation of micro-ball nanodiamond anvils for high-pressure studies above 6 Mbar | journal = Nature Communications | volume = 3 | issue = 1 | pages = 1163 | date = October 23, 2012 | pmid = 23093199 | pmc = 3493652 | doi = 10.1038/ncomms2160 | bibcode = 2012NatCo...3.1163D }}</ref> These anvils have reached pressures of {{val|600|u=GPa}}.<ref name="Wogan2012">{{Cite web |vauthors=Wogan T |publisher=Nature Communications |url=http://physicsworld.com/cws/article/news/2012/nov/02/improved-diamond-anvil-cell-allows-higher-pressures-than-ever-before |title=Improved diamond anvil cell allows higher pressures than ever before |work=[[Physics World]] |date=November 2, 2012 |access-date=July 1, 2022 |archive-date=January 2, 2018 |archive-url=https://web.archive.org/web/20180102123446/http://physicsworld.com/cws/article/news/2012/nov/02/improved-diamond-anvil-cell-allows-higher-pressures-than-ever-before |url-status=live }}</ref> Much higher pressures may be possible with [[nanocrystalline material|nanocrystalline]] diamonds.<ref name=Dubrovinsky/><ref name="Wogan2012"/>

==== Elasticity and tensile strength ====
Usually, attempting to deform bulk diamond crystal by tension or bending results in brittle fracture. However, when single crystalline diamond is in the form of micro/nanoscale wires or needles (~100–300{{nbsp}}nanometers in diameter, micrometers long), they can be elastically stretched by as much as 9–10 percent tensile strain without failure,<ref>{{cite journal | vauthors = Dang C, Chou JP, Dai B, Chou CT, Yang Y, Fan R, Lin W, Meng F, Hu A, Zhu J, Han J, Minor AM, Li J, Lu Y | display-authors = 6 | title = Achieving large uniform tensile elasticity in microfabricated diamond | journal = Science | volume = 371 | issue = 6524 | pages = 76–78 | date = January 2021 | pmid = 33384375 | doi = 10.1126/science.abc4174 | doi-access =  | bibcode = 2021Sci...371...76D | s2cid = 229935085 }}</ref> with a maximum local tensile stress of about {{nowrap|89–98 GPa}},<ref>{{cite journal | vauthors = Banerjee A, Bernoulli D, Zhang H, Yuen MF, Liu J, Dong J, Ding F, Lu J, Dao M, Zhang W, Lu Y, Suresh S | display-authors = 6 | title = Ultralarge elastic deformation of nanoscale diamond | journal = Science | volume = 360 | issue = 6386 | pages = 300–302 | date = April 2018 | pmid = 29674589 | doi = 10.1126/science.aar4165 | doi-access =  | bibcode = 2018Sci...360..300B | s2cid = 5047604 }}</ref> very close to the theoretical limit for this material.<ref>{{cite journal | vauthors = LLorca J | title = On the quest for the strongest materials | journal = Science | volume = 360 | issue = 6386 | pages = 264–265 | date = April 2018 | pmid = 29674578 | doi = 10.1126/science.aat5211 | arxiv = 2105.05099 | s2cid = 4986592 | bibcode = 2018Sci...360..264L }}</ref>