Are There Materials Harder Than Diamond?

Are there materials harder than diamond?

Yes. While naturally occurring, pure diamond remains the benchmark for hardness in the natural world, several synthetic or specially structured materials possess a hardness exceeding that of diamond (natural diamond typically has a Vickers hardness of approximately 70–100 GPa).

 

I. Materials Already Mass-Produced or Synthesized in Bulk, Exceeding Diamond in Hardness:
1. 1 Lonsdaleite (Hexagonal Diamond)
Composed of elemental carbon-just like ordinary diamond-Lonsdaleite features a hexagonal lattice arrangement rather than the cubic structure found in standard diamond.
High-purity synthetic bulk samples have achieved a hardness of 155 GPa-40% to 58% harder than diamond. (Note: Naturally occurring Lonsdaleite, typically found in meteorites, contains numerous impurities and consequently exhibits lower hardness.)

 

In 2025, a domestic research team successfully synthesized millimeter-scale, pure-phase bulk samples of Lonsdaleite. Exhibiting superior heat resistance and shear strength compared to diamond, it holds promise as a future raw material for high-end industrial abrasives and hard cutting tools.

 

1.2 Nanotwinned Diamond (Developed by the Tian Yongjun Team at Yanshan University)
By refining ordinary diamond into a nanoscale, ultrafine nanotwinned structure, researchers have achieved a hardness exceeding 200 GPa. This material currently represents the diamond variant with the highest potential for industrial application among all superhard materials, and small-batch production has already been successfully implemented; its performance significantly surpasses that of natural single-crystal diamond.

 

1.3 Wurtzite Boron Nitride (wBN)
A high-pressure polymorph of hexagonal boron nitride, wBN possesses a Vickers hardness of 75–85 GPa. Under high-pressure conditions, it is capable of scratching diamond. Furthermore, it is highly resistant to heat and does not react with steel alloys, making it vastly superior to diamond-based tools for machining iron-based workpieces.

 

2. Theoretical or Trace-Scale Laboratory Syntheses

(Currently Not Feasible for Mass Production, Yet Possessing Extremely High Hardness)

Carbyne (or Polyacetylene):

• This material consists of carbon atoms arranged in a linear, single-chain structure. Theoretically, its hardness is estimated to be 30 to 40 times that of diamond, and its tensile strength is approximately 200 times that of steel. However, it exhibits extremely poor chemical stability and can currently only be preserved in trace amounts when encapsulated within carbon nanotubes, rendering it unsuitable for practical, bulk-material applications.

 

High-Pressure Densified Carbon Nanotubes:

• While their hardness at ambient pressure is lower than that of diamond, after densification under a high pressure of 75 GPa, their hardness reaches 240 GPa-approximately four times that of diamond. Currently, they can only be synthesized under extreme laboratory conditions.

 

3. Frequently Confused With: Cubic Boron Nitride (cBN)
Standard cubic boron nitride possesses a hardness of 50–55 GPa. This is slightly lower than that of diamond, yet it ranks immediately below it, making it the second most widely used superhard abrasive in industry (commonly utilized in stone processing and cutting tools).