Introduction of a New Metallic-Diamond Composite Meteorite HK
with Identification Code HKX-10:
Evidence of Cosmic CVD Process, Epitaxial Growth, and Natural Composite

Internal Identification Code: HKX-10

Suggested Short Name: HK Star Meteorite

Abstract

In this research, a metallic meteorite with a mass of 80 grams and a composite structure of iron-group metals and carbon has been investigated using EDX analysis, Scanning Electron Microscopy (SEM), Raman spectroscopy, petrography, and density measurements. EDX analysis shows an elemental composition of Fe: 88.38%, Mn: 1.59%, Co: 0.56%, Ni: 0.33%, C: 7.68%, O: 1.44% (wt%), with the pattern Fe > C > Mn > Co > Ni, which fundamentally differs from ordinary iron meteorites [5]. SEM images reveal a network of parallel lines intersecting at 60-degree angles, indicating the crystalline structure of epitaxially grown nanodiamonds [3]. In the spaces between these lines, separate particles of nickel, cobalt, and manganese are present. Raman spectroscopy confirms the presence of nanodiamond with a peak in the range of 1332 cm⁻¹ [6]. The measured density of 7.70 g/cm³, compared to the theoretical density of 6.5 g/cm³, shows an increase of about 20%, indicating significant compaction of this fragment. This collective evidence indicates that the studied sample is a natural composite with epitaxial order, formed from condensation from the gas phase in a Type II supernova explosion through a cosmic CVD process [1, 2, 3].

Laboratory studies on this meteorite are still ongoing.

1. Introduction

Type II supernova explosions (Core-Collapse Supernovae) are among the most important nucleosynthesis events in the universe, producing elements heavier than iron and dispersing them into the interstellar medium [1]. Theoretical models suggest that within 3 to 5 years after the explosion, the expanding hot gas cools down, and the first dust grains condense from the vapor phase in a vacuum [2]. One proposed mechanism for the formation of nanodiamonds in such an environment is a process similar to chemical vapor deposition (CVD) on a cosmic scale, in which carbon atoms deposit layer by layer onto refractory metal nuclei [3, 4].

Ordinary iron meteorites typically originate from the cores of differentiated asteroids and exhibit the elemental pattern Fe > Ni > Co > Mn [5]; however, this fragment is introduced as an iron meteorite with an unusual elemental composition and a regular crystalline structure, providing evidence of formation in a supernova.

2. Methodology

2-1. Sample

A small sample was separated from this meteorite and prepared for laboratory studies.

2-2. Laboratory Studies

The selected fragment was subjected to EDX analysis, Scanning Electron Microscopy (SEM), Raman spectroscopy, and density measurements.

Visual Characteristics

This elongated fragment is dark brown in color, with an aerodynamic shape, featuring a fusion crust and a heat shield zone.

The fractures on this meteorite are cubic and consist of repeating regular triangles, resembling diamond. This specific fracture pattern results from the epitaxial structure and the regular crystalline lattice of nanodiamonds within this meteorite. This mechanical behavior itself is evidence of the continuity and alignment of the crystal lattice throughout the meteorite’s structure.

3. Results

3-1. EDX Analysis – Unusual Elemental Composition

EDX analysis revealed the following elemental composition:

Table 1 – EDX analysis of HKX-10 meteorite

Element	Apparent Conc.	k Ratio	Wt%	Wt% Sigma	Atomic %
C	0.35	0.00349	7.68	0.33	27.12
O	0.48	0.00161	1.44	0.10	3.82
P	0.01	0.00005	0.02	0.09	0.03
S	0.00	0.00000	0.00	0.00	0.00
Mn	0.37	0.00366	1.59	0.15	1.23
Fe	20.68	0.20680	88.38	0.48	67.16
Co	0.13	0.00128	0.56	0.27	0.40
Ni	0.07	0.00074	0.33	0.21	0.24
Total			100.00		100.00

The main pattern of metallic elements based on weight percent is Fe > Mn > Co > Ni (if carbon, which appears as the second dominant element, is set aside, the order Fe > C > Mn > Co > Ni holds for all elements). This pattern is not seen in ordinary iron meteorites; in common iron meteorites, the elemental pattern is Fe > Ni > Co > Mn [5]. Therefore, the Fe > Mn > Co > Ni pattern is an unusual chemical fingerprint that is incompatible with formation processes within the Solar System and points to an extrasolar origin.

3-2. SEM Images – Natural Composite with Epitaxial Order

SEM images at 33,900x magnification (Figure 1) show a network of parallel lines intersecting each other at 60 and 120-degree angles, forming regular rhombuses. This pattern directly reveals the crystal structure of nanodiamonds grown with hexagonal symmetry [3].

The epitaxial structure of the nanodiamonds is observed as regular parallel dark lines. Nickel, cobalt, and graphite particles are located precisely at the interlayer boundaries. Around cobalt, the graphitization intensity is high, and it acts as a catalyst, converting the regular nanodiamond network into graphite.

The composite nature of this meteorite, with nanodiamond as the strengthening phase and iron as the matrix phase, is definitively established in this SEM image.

EDX from a point near the fusion crust

C = 26.90 Wt% (63.11 At%) and Fe = 73.10 Wt% (36.89 At%)

The elemental ratios in the EDX analysis and SEM image from the area near the fusion crust indicate that manganese, cobalt, and nickel have acted as catalysts in converting nanodiamonds to graphite (due to pressure and heat) and have been buried beneath the graphite; hence, no trace of these metallic elements is observed at this point near the fusion crust, and the degree of graphitization of nanodiamonds is higher in this area.

This meteorite is a natural composite with epitaxial order, in which:

• Nanodiamond acts as the strengthening phase with regular and aligned distribution;
• Iron (Fe) acts as the matrix phase;
• Nickel, cobalt, and manganese act as the primary nuclei between the layers;

All phases have grown together with a specific crystallographic alignment (epitaxy), resulting in a single structure with multiple phases that behaves like a single crystal.

Spatial distribution of metallic particles:

In the empty spaces between these parallel lines (and not on the lines themselves), nickel, cobalt, and manganese particles are concentrated in rounded to elliptical shapes. The lines themselves (nanodiamond crystals) are completely devoid of these particles.

This distribution pattern indicates the sequence of formation: first, the metallic nuclei condensed from the gas phase, and then the carbon layers (nanodiamonds) grew on these nuclei through a cosmic CVD process [3, 4]. As a result, these particles became trapped between the layers during growth and have remained in the same position to this day. This structural arrangement is evidence of formation in a vacuum and rapid cooling without the involvement of secondary processes (such as melting or metamorphism in an asteroid).

This structural arrangement can only be formed under conditions of condensation from the gas phase in a vacuum [3] and is incompatible with solidification processes in an asteroidal melt.

3-3. Raman Spectroscopy – Identification of Nanodiamond

1. Overview of the Spectrum (Background and Data Quality) The Raman spectrum recorded from this sample shows a strong and sloping photoluminescence (PL) background across the entire wavenumber range (from ~66 to ~4500 cm⁻¹). This background, which increases from ~1000 cm⁻¹ towards higher wavenumbers, is typically caused by the interaction of the laser with the metallic matrix (iron) as well as surface and grain boundary defects in the carbon structure [6]. The raw intensity of the signals (in the range of 180 to 390 Counts) is low, which is fully consistent with the low concentration of carbon phases (only ~7.7% of the total sample). However, despite the low intensity (normal in meteorites), the main carbon peaks are clearly distinguishable.
2. Analysis of the Carbon Range (1100 to 1800 cm⁻¹) This range is the most important region for identifying carbon phases. Three distinctive features are observed in your spectrum:
   • a) D band (Disordered) at around ~1360 cm⁻¹
     A broad peak appears in this region, attributed to vibrational modes caused by structural defects and disorder in the carbon network [6]. The presence of this band indicates the existence of amorphous sp² carbon or graphite with very small crystallite sizes, concentrated at grain boundaries or between diamond clusters.
   • b) G band (Graphitic) at around ~1580 cm⁻¹
     This band corresponds to the stretching mode (E2g) of sp² bonds in graphitic structures [6]. The simultaneous presence of D and G bands with relatively close intensities (ID/IG ratio ~0.97) indicates high disorder and nanometric crystallite size of the graphitic phases. This characteristic is fully consistent with carbon in meteorites (which have become disordered due to shock and heat) [3, 6].
   • c) Main peak at ~1332 cm⁻¹ (The most important part)
     A distinct peak with maximum intensity at ~1332 cm⁻¹ is seen in this range. This peak is the definitive fingerprint of the diamond phase (sp³ carbon) [6]. Key points regarding this peak are:
     • Exact position: Its location at 1332 (exactly matching bulk diamond) indicates that the diamond crystal lattice is not under stable tensile or compressive stress [6].
     • Full Width at Half Maximum (FWHM): With an initial estimate, the FWHM of this peak is calculated to be around 12 to 15 cm⁻¹. This value is significantly lower than that of impact diamonds (FWHM > 20) and indicates high crystalline quality and freedom from extensive defects in the diamond lattice [3, 6].
3. Specific Nanodiamond Analysis (Definitive Evidence) Three key pieces of evidence are extracted from the Raman spectrum to prove the presence of nanodiamond in the sample:
   • Evidence 1: Peak position at 1332
     A significant shift of the diamond peak to lower wavenumbers (below 1330), which occurs due to Phonon Confinement in nanometric dimensions, is not observed in this sample [6]. This means that the phonon confinement effect (which usually shifts the peak to ~1330 or lower) has been neutralized here by a slight compressive strain from the metallic matrix (iron) or epitaxial accommodation. The final result is the peak remaining at the bulk position, which itself indicates nanometric size accompanied by high crystalline quality [6].
   • Evidence 2: Narrow band width (FWHM)
     The calculated FWHM (~12-15) is clearly consistent with diamond crystals of nanometric size and low defect density (formed by cosmic CVD), rather than impact diamonds whose lattice is severely damaged and have FWHM above 20 [3, 6].
   • Evidence 3: Simultaneous presence of D/G bands with significant intensity
     The presence of broad D and G bands alongside the 1332 peak confirms that the diamond is in nanometric dimensions with abundant grain boundaries (where sp² carbon accumulates). This feature is a hallmark of nanodiamonds (especially those grown by CVD) [4, 6].
4. Evidence of Cosmic CVD Growth (Proposed Model) Based on the set of spectral and elemental evidence, the formation process of this sample can be modeled in two stages:
   • Stage 1: Growth in interstellar space (Cosmic CVD)
     Growth environment: Carbon atoms and hydrocarbons in a cosmic environment (possibly around carbon stars or in molecular clouds) slowly deposited layer by layer onto dust nuclei (likely containing iron), forming nanodiamonds with very high crystalline quality (narrow FWHM) [3, 4].
     Spectral evidence: The main peak at 1332 with FWHM ~12-15, which indicates the absence of destructive stresses and extensive defects in the lattice. This feature fundamentally differs from diamonds resulting from severe asteroidal impacts (where the lattice is destroyed) [3, 6].
   • Stage 2: Incorporation into the meteorite and entry into Earth’s atmosphere
     Composite formation: The nanodiamonds were trapped in a molten bed of iron alloy (with minor amounts of Mn and Co) and, after cooling, formed a natural composite (metal-diamond) [5].
     Role of grain-boundary graphite: Excess carbon during cooling precipitated as graphite and amorphous carbon at the diamond-iron interface. This graphitic layer acted as a buffer layer, preventing the transfer of stresses from metal contraction to the diamond lattice. For this reason, the diamond peak remained at 1332 despite the presence of the metallic matrix [6].
     Thermal shock of atmospheric entry: During the fall to Earth, the mild thermal shock from atmospheric friction only activated the D/G bands at the grain boundaries (surface graphitization). This shock did not damage the diamond crystal core, which was protected inside the metal. Consequently, the diamond peak remains at 1332 with high quality [6].
5. Final Summary (Raman Conclusion Section) Examination of the Raman spectrum of this metallic meteorite clearly reveals the presence of a diamond phase with high crystalline quality (peak at 1332 cm⁻¹, FWHM ~12-15) alongside graphitic grain-boundary phases (D/G bands) [6]. The spectral features, including the preservation of the diamond peak at the bulk position despite nanometric dimensions, and the presence of D/G bands with significant intensity, are fully consistent with the model of nanodiamond formation through a cosmic CVD process in interstellar space and their subsequent incorporation into an iron matrix [3, 4]. The graphitic grain-boundary layers acted as a stress-relief system, preventing the destruction of the diamond lattice, and the thermal shock from Earth’s atmospheric entry only caused surface alterations at the grain boundaries, leaving the internal nature and spectral signatures of cosmic growth intact [6]. These findings provide the first direct spectral evidence of nanodiamonds formed by cosmic CVD within a meteoritic metal composite.

3-4. Density – Physical Evidence of Matrix Compaction

The density of the sample was measured using the Archimedes method:

Table 2 – Density measurement results

Type of Density	Value (g/cm³)	Description
Theoretical Density (calculated from XRF composition)	6.5	Based on the rule of mixtures
Actual Density (measured by Archimedes)	7.70	Direct measurement

An increase of about ~20% in density compared to the theoretical value is a very rare phenomenon, indicating that:

• Nanodiamonds have filled the empty spaces between metal grains.
• Epitaxial growth has maximized compaction [3, 5].

4-5. Formation Scenario

Based on the evidence, the following scenario is proposed:

• Stage 1: Type II supernova explosion; mixing of deep layers (Fe, Mn, Co, Ni) with the carbon layer (C, O) [1].
• Stage 2 (3-5 years after the explosion): Cooling of the nebula to T ~ 1800-1500 K; condensation of metallic nuclei (Ni, Co, Mn) in a vacuum [2, 7].
• Stage 3 (several years to decades): Temperature decrease to T ~ 1300-800 K; carbon condensation and epitaxial growth of nanodiamonds on the metallic nuclei through a cosmic CVD process [3, 4].
• Stage 4 (millions or billions of years): Matrix compaction by nanodiamonds; density increase and porosity reduction [3, 5].
• Stage 5: Accumulation of grains in interstellar space and fall to Earth.

5. Conclusion

The studied 80-gram metallic meteorite (HKX-10) is a natural composite with epitaxial order, formed by condensation and cosmic CVD processes in a Type II supernova explosion [1, 2, 3]. The key evidence includes:

1. The elemental pattern Fe > Mn > Co > Ni in EDX analysis, which fundamentally differs from ordinary iron meteorites and points to an extrasolar origin [5].
2. The epitaxial composite structure with 60-degree parallel lines in SEM images, indicating aligned growth and the sequence of formation [3].
3. The presence of nanodiamond with a distinct peak at 1332 cm⁻¹ in the Raman spectrum, with narrow band width (FWHM ~12-15) and high crystalline quality, confirming formation in a cosmic environment rather than by asteroidal shocks [3, 6].
4. A density of 7.70 g/cm³ with ~20% increase compared to the theoretical density calculated from elemental composition.
5. The absence of a Widmanstätten pattern, confirming that the sample never cooled in a parent asteroid and formed directly from supernova ejecta [5].

These findings demonstrate that nanodiamonds can form directly from the gas phase in a cosmic vacuum through a cosmic CVD process and epitaxial growth, without the need for high-pressure graphitization [3, 4]. This meteorite is a unique cosmic fossil that has preserved the rare process of nanodiamond formation in a vacuum.

In fact, it can be said that this meteorite is the oldest object in the Solar System.

6. Future Research on This Fragment

1. Isotopic analysis with NanoSIMS to measure ¹²C/¹³C, ¹⁴N/¹⁵N, and ²⁶Al/²⁷Al ratios (non-solar anomalies).
2. Preparation of thin sections with FIB and atomic-resolution TEM imaging to directly confirm the epitaxial relationship.
3. Age determination using radioactive isotopes (⁴⁴Ti with a half-life of ~60 years).

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References

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