Where is Meteoritic Breccia/Conglomerate (Thin Section) found?
Breccia or Conglomerate (likely meteorite) in thin section, viewed under plane-polarized light (PPL) and cross-polarized light (XPL)
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Open the appMeteoritic Breccia/Conglomerate (Thin Section) occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Meteoritic Breccia/Conglomerate (Thin Section)
Antarctica
Major collection site for meteorites due to ice flow concentrating specimens and preserving them in a pristine state. Many meteoritic breccias and conglomerates have been recovered here.
Sahara Desert (North Africa)
Vast, arid regions where meteorites are well-preserved and easily spotted against the sand. Numerous meteoritic breccias, including lunar and Martian meteorites, have been found.
Oman
Similar to the Sahara, the arid environment aids in meteorite preservation and discovery.
Australia (Nullarbor Plain)
Flat, arid limestone plain where meteorites are concentrated and well-preserved.
Impact Craters (worldwide)
While the breccia itself is meteoritic, fragments of meteorites can be found within terrestrial impactites at impact sites (e.g., Ries Crater, Germany; Sudbury Basin, Canada), though these are typically highly altered.
Collecting tips
- Microscopic Examination is Key. Identification as 'likely meteoritic' is almost exclusively done through petrographic analysis of a thin section. Macroscopic identification of a breccia as meteoritic is extremely difficult without prior knowledge or context.
- Look for Unique Mineralogy. Search for unweathered Fe-Ni metal (kamacite, taenite), troilite (FeS), and unique high-pressure mineral phases (e.g., ringwoodite, majorite, maskelynite) which are strong indicators of extraterrestrial origin or impact shock.
- Identify Chondrules. The presence of chondrules (spherical to sub-spherical silicate aggregates) is a definitive indicator of a chondritic meteorite, many of which are brecciated.
- Recognize Shock Metamorphic Features. Look for features like planar deformation features (PDFs) in quartz or feldspar, mosaicism in olivine/pyroxene, undulatory extinction, and maskelynite (diaplectic glass after plagioclase). These indicate high-pressure shock events characteristic of impacts.
- Assess Texture and Clast Composition. Observe the angularity/roundness of clasts, the polymict nature (multiple rock types), and the composition of the clasts. A mix of different meteoritic lithologies or mineral fragments is common in breccias.
- Consider Terrestrial Contamination/Alteration. Be aware of terrestrial weathering products (e.g., rust from metal oxidation, clay alteration of silicates) which can obscure primary meteoritic features. Unweathered metal and troilite are good signs.
Quick Check
- Color:
- Variable, often dark matrix with lighter clasts; opaque metal/troilite.
- Luster:
- Not applicable for thin section; constituent minerals have vitreous to metallic luster.
- Streak:
- Not applicable for thin section; individual minerals would have their characteristic streak (e.g., grey for metal, black for troilite).
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