Lonsdaleite

Chemical formula: C

Lonsdaleite is a hexagonal polymorph of diamond, formed by meteorite impacts, theoretically distinguished by higher hardness.

## Characteristics Lonsdaleite, also known as hexagonal diamond, is an allotropic form of carbon, similar to graphite and diamond. Its crystal structure is hexagonal, in contrast to the regular (cubic) structure of typical diamond. This mineral forms under conditions of extremely high pressure and temperature, such as those present during a meteorite impact on the Earth's surface. Natural lonsdaleite crystals are microscopic in size and usually occur as tiny, dispersed grains within graphite in iron meteorites. Specimens are most often brownish-yellow or grayish in color. ## Physical Properties Lonsdaleite is characterized by exceptional hardness, which, according to theoretical simulations, may exceed that of diamond. In practice, due to the microscopic size and impurities of natural crystals, these measurements are difficult to verify. The hardness of natural samples is estimated at 7-8 on the Mohs scale. The mineral's density is approximately 3.2 g/cm³. Crystals are transparent. ## Colors and Varieties This mineral occurs in a limited range of colors, most often as brownish-yellow or gray. Due to its specific structure and genesis, no colored or commercial varieties are distinguished. ## History and Name Lonsdaleite was first identified and described in 1967 in the Canyon Diablo meteorite, found near Meteor Crater in Arizona (USA). Its name honors the British crystallographer, Professor Kathleen Lonsdale, a pioneer in the field of crystal structure research using X-rays, who confirmed the hexagonal structure of this mineral. ## Applications Due to the extreme rarity and microscopic size of natural crystals, lonsdaleite currently has no industrial applications. Its significance is purely scientific and collectible, as a unique extraterrestrial material.

Properties

Mohs hardness: 7-8
Luster: Adamantine
Density: 3.2
Transparency: Transparent
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of lonsdaleite is impossible without advanced laboratory techniques such as X-ray diffraction (XRD) or transmission electron microscopy (TEM). In collecting conditions, identification relies on confirming that the specimen is a fragment of a meteorite in which the presence of this mineral has been confirmed (e.g., Canyon Diablo). ## Distinguishing from Similar Minerals Lonsdaleite is closely related to diamond and graphite. It differs from diamond by its hexagonal crystal structure (in contrast to diamond's regular structure). It differs from graphite by its significantly greater hardness and transparency. In practice, it occurs as microscopic inclusions in graphite within meteorites. ## Crystal Forms Lonsdaleite forms exclusively microscopic, hexagonal crystals, often with imperfect development. It occurs as fine grains, aggregates, and inclusions in graphite.

Geological environment

## Genesis Lonsdaleite forms as a result of shock metamorphism. When a graphite-bearing meteorite impacts Earth, the immense pressure and high temperature generated at the moment of impact cause the transformation of graphite's structure into the hexagonal structure of lonsdaleite. This process occurs in a fraction of a second. ## Mineral Associations This mineral occurs almost exclusively in association with graphite, diamond, troilite, cohenite, and other minerals typical of iron meteorites. ## Localities The most important and type locality for lonsdaleite is the Canyon Diablo meteorite from Meteor Crater in Arizona, USA. Its presence has also been confirmed in other meteorites, such as Kenna (New Mexico, USA) and Allan Hills 77283 (Antarctica).

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the value of a specimen does not lie in the visual characteristics of lonsdaleite itself (which is invisible to the naked eye), but in the authenticity and provenance of the meteorite fragment in which it was identified. Specimens with laboratory-confirmed presence of lonsdaleite, originating from known falls like Canyon Diablo, are highly valued. The size and history of the meteorite fragment itself also play a key role. ## Popular Localities The only source of specimens available on the collector's market are meteorite fragments. The most classic and desired material are specimens from the Canyon Diablo meteorite, which were the first to be used to describe this mineral.

Care and storage

## Cleaning Specimens containing lonsdaleite (usually meteorite fragments) are stable and do not require specialized cleaning. If necessary, dust can be removed with a soft brush or compressed air. Wet cleaning should be avoided to prevent damage to the meteorite matrix. ## What to Avoid Avoid contact with strong chemicals that could react with associated minerals in the meteorite. Although lonsdaleite itself is very hard and resistant, meteorite specimens can be sensitive to moisture and sudden temperature changes. ## Storage Meteorite fragments with lonsdaleite are best stored in a dry place, in a sealed container or display case, to protect them from dust and moisture. Due to their scientific value and rarity, minimizing direct contact is recommended.