Meteorite — A Postcard from the Early Solar System
Meteorites are pieces of asteroids (and occasionally the Moon or Mars) that survived the plunge through Earth’s atmosphere and landed—sometimes loudly—in our fields, deserts, ice, or streets. In hand, they’re heavier than they look, often skin‑darkened by a thin fusion crust, and full of textures that read like cosmic diary entries: chondrules (little beads), metal flakes, shock veins, and in some irons, the famous Widmanstätten patterns. If rocks were storytellers, meteorites would begin every tale with “A long time ago, in a nebula far, far away…”
Identity & Vocabulary 🔎
Meteor vs. meteorite vs. meteoroid
Meteoroid is the object in space. Meteor is the bright streak as it ablates in the atmosphere. Meteorite is the piece that reaches the ground. Easy way to remember: add air (meteor), add Earth (meteorite).
Falls vs. finds
A fall is witnessed as it lands and recovered promptly (fresh, intact fusion crust). A find turns up later during searches or by chance and may show weathering (rust, desert varnish).
What Kinds Exist? 🧭
| Group | Subtypes | How to Recognize | Typical Density |
|---|---|---|---|
| Stony — Chondrites | Ordinary (H, L, LL), Carbonaceous (e.g., CV, CM), Enstatite | Often chondrules (mm‑sized spheres); fine metal flakes; dark fusion crust | ~3.3–3.7 g/cm³ |
| Stony — Achondrites | HED (Vesta‑linked), Lunar, Martian, others | No chondrules; igneous textures (basaltic or cumulate); metal sparse | ~3.0–3.5 g/cm³ |
| Stony‑iron | Pallasites (olivine + metal), Mesosiderites (breccias) | Metal framework with gemmy olivine (pallasite) or mixed rock‑metal fragments | ~4.5–5.5 g/cm³ |
| Iron | Octahedrites, Hexahedrites, Ataxites | Mostly Fe‑Ni metal; thumbprint regmaglypts; etched slices show Widmanstätten patterns | ~7.5–8.0 g/cm³ |
How Meteorites Form 🌌
Chondrites — the primordial mix
Chondrites are time capsules of the solar nebula: dust clumped and briefly melted into chondrules, sprinkled with older CAIs (calcium‑aluminum inclusions), then compacted into rock on small asteroid parent bodies.
Achondrites — igneous offspring
Some parent bodies heated up (radioactive decay, collisions), partially melted, and built crusts and mantles. Ejecta from these worlds cooled as achondrites—basaltic or plutonic rocks without chondrules. Famous families: HED (linked to asteroid Vesta), plus lunar and martian meteorites.
Irons & stony‑irons — planetary metallurgy
Deep inside larger asteroids, metal segregated to form cores. Later impacts excavated and delivered iron meteorites. Interface zones of metal and silicate became stony‑irons—pallasites (olivine set in metal) and mesosiderites (rock‑metal breccias).
One solar system, many stories: dust beads, volcanic crust, and alien metalwork—all landing in your collection tray.
Appearance & Field Clues 👀
Exterior hints
- Fusion crust: thin, dark rind from atmospheric heating; can be glossy when fresh, matte and cracked when weathered.
- Regmaglypts: “thumbprints” on irons and some stony masses—sculpted by ablation.
- Shape: rounded edges, occasional oriented forms with flow lines on one face.
- Heft: heavier than common rocks of similar size.
Interior tells (on broken/cut surfaces)
- Chondrules: mm‑sized beads in a dark matrix—classic chondrite sign.
- Metal flakes: bright specks/veins of Fe‑Ni; may rust brown if weathered.
- Shock veins: thin, dark melt veins from impacts in space.
- Pallasite jeweling: honey‑colored olivine crystals in a metal network.
- Irons: solid metal; slices etched by specialists reveal Widmanstätten geometry.
Photography: Side‑light ~30° rakes across regmaglypts and flow lines; back‑light thin slices to make chondrules or olivine glow.
Under the Loupe / Saw 🔬
Chondrites
At 10×, chondrules show porphyritic textures (tiny crystals) or fine barred patterns. Metal appears as reflective grains; sulfide (troilite) as bronzy flecks.
Achondrites
Expect igneous textures—interlocking plagioclase, pyroxene, olivine—without chondrules. Some lunar pieces show vesicles and glassy impact melt pockets.
Irons & stony‑irons
Polished, professionally etched iron reveals interleaving kamacite/taenite lamellae (Widmanstätten). Pallasites display sharp olivine boundaries; mesosiderites look like a tumbled rock‑and‑metal salad.
Look‑Alikes & How to Tell 🕵️
Industrial slag & clinker
Often bubbly or ropey with vesicles; glassy surfaces; sometimes magnetic. Meteorites rarely have true vesicles and look denser, more “metal‑rock” than foam.
Hematite/magnetite nodules
Very heavy and can attract magnets, but interiors are uniformly metallic or earthy—no chondrules or Fe‑Ni metal flakes. Streak tests (red for hematite) identify them, though streaking can mar a specimen.
Basalt & dark lavas
Fine‑grained, sometimes with vesicles and visible feldspar/pyroxene microlites; lacks fusion crust character and metal specks.
Concretions & “desert varnish” rocks
Brown/black skins from weathering can mimic fusion crust, but broken surfaces show sedimentary textures, not meteoritic fabrics.
Tektites & obsidian
Natural glass (impact or volcanic): vitreous, often pitted or flow‑banded, no metal, and much lower density than irons/stony‑irons.
Checklist for confidence
- Fusion crust present (thin, dark rind, not thick glaze).
- Heftier than local rocks.
- Metal flecks or olivine + metal (for pallasite).
- No bubbly vesicles; magnet often attracts (but not always).
Notable Meteorites 📚
Allende (Mexico, 1969)
A carbonaceous chondrite famous for abundant CAIs—some of the oldest solids in the solar system. A favorite classroom slice: it looks like a starry sky in stone.
Murchison (Australia, 1969)
Another carbonaceous classic, rich in organic compounds and presolar grains—tiny stardust older than the Sun embedded in a rock you can hold. Mind‑bending.
Hoba (Namibia)
The largest known single meteorite mass on Earth, an iron so huge it politely decided to stay put. Great for perspective: sometimes the sky delivers in bulk.
Sikhote‑Alin (Russia, 1947)
An iron fall that produced sculptural shrapnel and regmaglypted masses. Many pieces show sharp flow lines—textbook aerodynamic art.
Campo del Cielo (Argentina)
Iron masses scattered across a field; common in collections and great to demonstrate regmaglypts and heft.
Chelyabinsk (Russia, 2013)
A modern, well‑documented chondrite fall with dash‑cam fame—reminder that the solar system still says hello now and then.
Care, Storage & Display 🧼
General handling
- Keep dry. Moisture is the enemy of iron phases; use silica‑gel packs in display cases.
- Handle with clean, dry hands or gloves—skin oils encourage rust on irons and metal‑rich stones.
- Don’t scrub the fusion crust; it’s part of the specimen’s history.
Irons & stony‑irons
- Store in low humidity; avoid bathrooms, kitchens, ocean air.
- Light microcrystalline wax can help seal a polished surface (many dealers use it). Reapply sparingly.
- If orange spots appear, isolate the piece, dry thoroughly, and consult conservation guides or a professional preparator.
Stony meteorites
- Keep slices in airtight sleeves or display frames.
- Label provenance clearly—falls/dates/locations matter for science and value.
- For thin sections: avoid fingerprints; store flat in labeled slide boxes.
Questions ❓
Are meteorites radioactive?
Not in any unusual way. Most sit at background levels comparable to terrestrial rocks.
Will a magnet always stick?
Many meteorites are magnetic due to Fe‑Ni metal, especially irons and ordinary chondrites. Lunar and martian meteorites can be weakly magnetic or essentially non‑magnetic—lack of pull doesn’t rule out a meteorite.
What’s that geometric pattern in iron slices?
The Widmanstätten pattern—intergrowth of kamacite and taenite that formed during extremely slow cooling in an asteroid’s core. It shows up after careful etching of a polished slice.
Is density a good test?
Roughly, yes. Irons are very dense; chondrites feel heavier than similar‑sized Earth rocks. But it’s one clue among many.
How can I be sure?
Combine field clues (fusion crust, chondrules/metal, heft) with expert testing. Labs can check nickel content and textures non‑destructively (e.g., XRF, microscopy). Paperwork and a clear chain‑of‑custody matter.
Small joke to close: meteorites are the universe’s “you up?” texts—occasionally dramatic, always fascinating.