Lunar and Planetary Science XXXI 1075.pdf

ELECTRON MICROSCOPY EVIDENCES OF NOVO UREI DIAMOND NATURE A.A. Valter 1, H..S. Oleynik 2 , A.V. Fisenko 3 , L.F. Semenova 3 Institute of Applied Physics Nat. Acad. Sci of Ukraine; 2-Institute of Material Science Problem Nat. Acad. Sci. of Ukraine; 3 - Institute of Geochemistry and Analytical chemistry Russian Acad. Sci.

One of the most important discovery in meteoritics of and turning of packets of layers are present. XIX century - ureilite type of stony meteorite and Two or /and three phases particles are similar to the diamond in it [1] is not completely understood even graphite ones. Presence of the dense carbon phase (es) now at the end of XX century. We try to obtain a new was distinguished by SAD. The triple lonsdaleite tex- knowledge in this field by the TEM and SEM investi- ture with [1120] graphite// [0001] lonsdaleite was gation of Novo Urei (NU) meteorite diamonds and by determined. One can see a splitting of (100) graphite comparison of the results with the achievements in reflection in three directions (through 120o)(fig.3). study of artificial and nature micro diamonds with The new reflections correspond to interplaner dis- known origin. tances 2,04 - 2,07 A. This is close to (0002) for lons- The diamond bearing fraction was obtained by hard daleite and (111) for cubic diamond. So, the observed chemical treatment of NU meteorite material includ- orientation is (100) grapfite//(001) lonsdaleite and (or) o ing HClO4 action at 200 C [2]. The grain sizes of (111) diamond. fraction which was received vary from apx. 0.5 to 15 Conclusions. mcm. 1.The layer structure of diamond micro crystals with The X-ray powder pattern and statistics of electron the signs of layer rotation and the orientation of lay- selected area diffraction (SAD) study of individual ers to (110) of diamond are the strong evidence of it grains show that monophase diamond is the principal origin upon graphite under shock compression. part of our sample and forms a larger grains, but par- 2.How it is revealed by structure investigation of ex- ticles of graphite and graphite - lonsdaleite (+ dia- perimentally obtained material [3], orientation (110) mond ?) growthes also exist. diamond//(0001) graphite (I) is formed by two step The diamond grains are layer plates with fragments of martensite - like transformation: graphite - lonsdaleite hexagonal outlines (fig.1). One can see on perpendicu- and lonsdaleite - diamond . Such phase orientation, as lar to plates surface splits more thick layers (up to 0.2 a result of shock induced carbon transformation is mcm) divided by more friable (more porous) and thin usual in experiment [3] but rarely observed in Earth ones (fig. 2). SAD of diamond grains have a point impact diamonds, and every time it accompanied by character some times with Kikuchi lines. The single another one (111) diamond//(0001) graphite (II) [4]. dislocations and in one case a group of dislocations Orientation (I) was also reproduced by short time (10 - were also observed. Such relatively perfect cubic dia- 3s) static loading [3]. The thin diamonds twins on mond micro crystals represent individual layers (111) are obviously forms by rapid graphite or (and) (fig.1,2) with strong orientation to (110) of diamond lonsdaleite transformation to diamond [3]. structure. The layers are turned one to another round 3.The origin of cubic NU diamonds with relatively [110] at 20-25o. perfect structure one can explain by comparison with In some diamond crystals micro twins by one or two cubic varieties of impact diamond from Popigai crater planes of {111} system are observed. On SAD pictures [4,5] by natural annealing under the conditions of a sometimes diffraction strips along [111] are also ob- great scale impact: such as Popigai crater formation served which detected a diamond structure disorder in or grater. One can assumes that orientation (1) which this direction. differ from the common one of Earth impact diamonds The graphite also forms a plate-like grains with usual may be also a result of a great scale of impact. orientation to (0001). As a rule they are some smaller 4.The observed graphite grains, if they genetically than the diamond one: 0,5 - 2 mcm. The graphite connected with diamonds may be in general secondary grains usually consists from a little fragments. By formed by the retrograde diamond-graphite transition SAD one can reveal from 2 to apx. 20 fragments per by the residue high temperature action. Such fragmen- 0.5 mcm2. In more perfect microcrystals the moire tal grains with the different planes of surface orienta- patterns were observed which are evidences of (0001) tion (0001) or (1120) we earlier observed in experi- layers turning round [0001] axis. The strips on SAD mentally in recovery graphite upon shock produced pictures from strong reflections (100) to (101) are also diamond. By (100) to (101) SAD strips of graphite observed. one can assume an evidence of before transformation In the graphite grains fragmentation by the bending shock wave action. Lunar and Planetary Science XXXI 1075.pdf

Novo Urei diamond: A.A.Valter et.al.

5.Two or three phase carbon particles can be also ei- ther a product of not full shock transformation of Fig.2 NU diamond graphite to the robust carbon forms, or a result of very TEM picture ⊥to (110) layers quickly cooling of high temperature heated graphite Scale - 0.25 mcm [6].

The revealing of the points 4 and 5 require the additional investigations of grains with definite loca- tion in meteorite structure. References.1.Jerofeieff M ., Latchinoff P. Proc. St.-Peterburg Imperial Mineral. Soc.,1888, 24, p.263.2.Fisenko A.V. et al. LPSC Ab- stracts,XXIV,pt.1,1993,p.485.3.Kourdjumov A.V. et al. Polymorphic modifications of carbon and boron nitride. Reference book. Moscow, 1994, 320 p (in Russian). 4. Valter A. A. et al .Shock metamorphoge- netic carbon minerals. Kiev, 1992, 171 p.(in Rus- sian).5. Erjomenko G.K. et al. Abstracts of 26th Ver- nadsky-Brown Microsymposium of Comparative Planetology, Moscow, 1997,p.35.6.Fedoseev D.V. et al. Journal of Phys. Chem., 1982, 56, N 6,p.1517 (in Russian).

Fig 3 SAD picture of two or three phase NU carbon particles. Arrow points (100) grafite + (111) diamond and(or) (002) lonsdaleite reflections.

Fig 1. NU diamond SEM picture. Scale - 2 mcm