Lonsdaleite

• IMA 1966-044

Lonsdaleite, often referred to as hexagonal diamond is a very rarely occurring mineral from the mineral class of elements and a very rare form of carbon. It crystallizes in the hexagonal crystal system and is fine-grained, cubic or cuboctahedral units and polycrystalline aggregates of diamond.

Etymology and history

First found and described lonsdaleite 1967. It is named in honor of the Irish Kristallografin and Professor Kathleen Lonsdale.

Classification

In the old ( 8th edition ) and new classification of minerals ( 9th Edition ) by Strunz is the lonsdaleite in the department of " semi-metals and non-metals " sorted. The new scheme is divided here, however further. Lonsdaleite heard now ( so far without recognition by the IMA / CNMNC ) to, graphite, diamond and silicon of " carbon-silicon - family " together with Chaoit, fullerite.

The classification of minerals according to Dana represents the lonsdaleite also with diamond, graphite, and Chaoit fullerite in the "carbon polymorph group" the Department " Native element with semi-metallic and non- metallic elements" ( translation: " Polymorphic carbon group " the department " Dignified elements with semi-metallic and non-metallic elements ").

Education and Locations

Lonsdaleite arises when the graphite is converted by shock events, ie at high pressure and high temperature in a diamond-like structure, but here, the hexagonal crystal lattice of graphite is maintained. Such conditions prevail, for example, with impacts on the meteorite parent body.

Type locality for the mineral is the environment of the Barringer Crater and found there Canyon Diablo meteorite. Other localities are the iron meteorite Allan Hills 77283, the Ureilit Kenna, and a kimberlite field in China. Lonsdaleite is increasingly encountered together with graphite and diamond in ureilites, a subspecies of the achondrites.

Crystal structure

Lonsdaleite crystallizes in the hexagonal crystal system in space group P63/mmc with lattice parameters a = 2.52 Å and c = 4.12 Å and four formula units per unit cell.