Sahara
97037

Inside a
shock-melt vein.

LL7 ORDINARY CHONDRITE

A petrographic, geochemical and spectroscopic investigation of an unusual LL7 ordinary chondrite and the shock-melt vein preserved within it.

Sahara 97037 specimen photographed with collection label and 1 cm scale marker — Sahara 97037 specimen · introductory presentationPhoto credit in presentation: Van de Gehuchte Erik

01 / SPECIMEN → THIN SECTION

A dark line.
A deeper question.

Sahara 97037 is an LL7 ordinary chondrite. LL refers to the low-iron, low-metal group; type 7 records intense thermal processing, with original chondrule textures largely erased.

In transmitted light, a nearly opaque vein approximately 2.9 mm thick cuts sharply through the olivine-dominated host. What created it, and what happened to the material beside it?

A polished Sahara 97037 sample mount held between fingers — The mounted sampleRevised research poster

A dark, nearly opaque vein cuts across the host. The full original field is retained. — A vein through the thin section~2.9 mm vein thickness reported in the abstract; image bar text unreadable

02 / VEIN → MINERAL TEXTURES

At the margin,
the texture changes.

Within the vein, SEM imaging reveals fine-grained, euhedral olivine and pyroxene, approximately 10–25 μm across, with melt textures.

Immediately beside the vein, grains are larger: approximately 50–100 μm, with granoblastic textures. The contrast helps constrain how the vein affected its surroundings.

Coarser grains on the left meet fine-grained material on the right across the vein margin. — The vein margin100 μm bar in original

Petrography, BSE imaging, and reported compositions

Optical petrography used an Olympus BH2 microscope. Backscattered electron imaging used a Hitachi S4700 field emission scanning electron microscope.

The detailed abstract reports pyroxene at En₉₇ and two olivine compositions, Fo₉₅ and Fo₆₅, within the vein. These are reported analytical findings, not compositions inferred from image brightness.

↗ Detailed abstract · methods and results

03 / TEXTURE → CHEMISTRY

The chemistry
has a geography.

Full-section maps preserve the relation between the vein and its host. Explore the magnesium signal and the Fe/Ni/S composite, with their original scale bars intact.

Brighter regions represent relatively greater Mg signal, darker regions relatively lower Mg signal. — Three regions in magnesium1 cm bar in original

Three chemical regions.

The Mg map distinguishes the host, the vein, and the coarser granoblastic material beside it. Brighter pixels indicate relatively greater Mg signal.

The abstract reports slight Mg enrichment in the vein and stronger enrichment immediately alongside it. These are relative spatial differences; the image is not a calibrated concentration readout.

EPMA / WDS mapping details

Analyses used a five-spectrometer Cameca SX5-Tactis at the American Museum of Natural History. Wavelength dispersive spectroscopy was used for quantitative point analyses and elemental mapping.

Mapping parameters: 40 nA beam current, 15 ms dwell time, 6 μm step size. The full section is a mosaic of 15 EPMA maps, collected over three passes of five elements.

The abstract contains an inconsistent unit in its point-analysis voltage sentence. That voltage is left unreported here; see research notes.

04 / CHEMISTRY → STRUCTURE

Read the minerals
through light.

Raman analysis identifies four phases within the vein. The distinction between an identification and a qualified interpretation remains part of the story.

The unmodified Raman image from the revised research poster. — Four phases within the vein20 μm bar in original; 751 nm reported mapping resolution

Four vertically offset spectra with the original phase legend and axes. — The original Raman spectraRaman shift (cm⁻¹); intensity in original units

PHASE 1 / SPECTRAL EVIDENCE

Olivine

845 · 820 cm⁻¹

Smaller feature near 912 cm⁻¹.

The dominant pair of bands supports an olivine identification.

Band positions follow the detailed abstract. The displayed plot retains the original curves and axes; selecting a phase changes the explanation.

Raman mapping details

WiTec Alpha300R confocal Raman microscope; 532 nm laser at approximately 20 mW; 0.7 second integration; 300 grooves/mm spectral grating. Reported mapping resolution: 751 nm.

The detailed abstract places “likely clinoenstatite” with phase 2 and describes phase 4 as fine-grained pyroxene. This takes priority over the less specific poster caption.

↗ Detailed abstract · Raman results

05 / INTERPRETATION → OPEN QUESTIONS

Melting leaves
more than a vein.

The working interpretation

The large vein is interpreted as a shock-melt vein. Its fine-grained textures are consistent with crystallization from melt; the coarser granoblastic material near the margin is interpreted as localized contact metamorphism associated with that vein.

This connects the mineral record to both shock and thermal overprinting in a highly processed LL chondrite.

The investigation continues

Wadsleyite and ringwoodite had not yet been observed in the studied vein. That is an observation within the scope of this investigation, rather than proof of their absence throughout the meteorite.

The abstract identifies continued structural analysis of the vein margin as ongoing work. The pyroxene identification remains qualified as likely clinoenstatite.

THE RESEARCH, IN FULL