Diamond Research

Hexagonal Diamond: What the 2025 Synthesis Study Found

Researchers in China reported producing well-crystallised hexagonal diamond by heating compressed graphite. The work offers a new route to studying this unusual form of carbon, but its laboratory results should not be confused with a finished commercial material.

A note on the “40% stronger” headline

Strength and hardness describe different material properties. A single percentage should not be used as a universal comparison unless the test method and the property being compared are clearly stated. This article therefore focuses on the reported synthesis and findings rather than presenting “40% stronger” as a settled, general result.

What is hexagonal diamond?

Most familiar diamond has a cubic crystal structure. Hexagonal diamond, also known as lonsdaleite, refers to a form of carbon with a different, hexagonal arrangement. The distinction is about atomic structure; it does not mean that every material described as lonsdaleite has the same purity, size or measured properties.

ICIA has a short overview of lonsdaleite and its relationship to diamond.

What the reported study investigated

The research team described a method that heats highly compressed graphite and promotes the formation of a post-graphite phase. The researchers reported producing a millimetre-scale block of hexagonal diamond and measured a hardness of 155 GPa for their sample.

This is a result from a particular experimental sample and method. It should not be treated as a guarantee that all hexagonal diamond is harder than all conventional diamond, or that the material is already widely available.

How it differs from conventional diamond

Crystal arrangement

Conventional diamond has a cubic crystal structure. Hexagonal diamond has a hexagonal structure. Both are forms of carbon, but the arrangement of their atoms differs.

How properties are reported

Hardness, strength and stiffness are not interchangeable measures. A meaningful comparison needs to identify the property tested, the sample and the testing conditions.

For an introduction to conventional diamond terminology, see ICIA’s 4Cs of Diamonds guide .

Potential uses—and what remains uncertain

The research points to possible future interest in applications that use hard materials, such as cutting, drilling and polishing. These are potential directions for further development, not proof that hexagonal diamond is ready to replace conventional diamond in tools, electronics or jewellery.

Researchers need to study how the material can be produced consistently and at useful scale.
Performance must be assessed for the specific application and operating conditions.
Availability, cost, durability and manufacturing requirements remain practical questions.

What jewellery buyers should know

A research report about a new carbon structure does not by itself indicate that hexagonal diamond is being sold as a jewellery gemstone. If a seller uses terms such as “super diamond” or “lonsdaleite”, ask what material is being offered and what documentation supports that description.

Do not assume that a hardness claim alone establishes a stone’s identity, quality or suitability for a particular use. For conventional diamond grading concepts, consult the ICIA 4Cs guide .

This article summarises a reported research development for general information. Laboratory measurements do not establish commercial availability or determine the value of a jewellery item.