Telescope Reviews: Dumb Question

Mark,

In a nutshell, chemistry.

When dealing with "unclassifieds", it's a matter of experience and provenance.

There are elements and minerals in meteorites that do not match Earthly chemistries. The presence of nickel is a strong indicator of meteoritic origin. Sure, nickel is present in the Earth, but most of it is deep down near the mantle - and what is present in the mines of the Earth's crust does not appear in the same form as meteoritic nickel-iron. In other words, meteorites (stone or iron) do not match any Earthly metallic ores.

Some stony meteorites can resemble Earth rocks - especially older weathered meteorites which have lost their distinctive fusion crust. In these cases, the presence of nickel is the major determining factor. Some Earthly rocks can mimic stony meteorites - but these rocks are so rare, that they are valuable just like a meteorite. And even these are less dense than meteoritic stones. A keen eye, a magnet, a beaker of water, and a scale can weed out the meteorites from a pile of suspect specimens. Streak testing is also used - a common practice amongst rock and mineral hounds.

When dealing with unknown specimens, it's best to rely on a reputable dealer with credentials. IMCA or Meteoritical Society membership is a good sign that the dealer takes their business seriously. I have bought and sold alot of meteorites in my time, and I have never purchased a bogus rock (or "meteorwrong") from an IMCA or MS member.

Finding meteorites in the field is a whole different ballgame. Determining whether a specimen bought from a dealer or another collector is genuine is relatively easy because the specimen has been vetted to some degree. But, going out into the field and identifying a meteorite from a dry stream bed that is strewn with dark colored rocks, is more difficult. Some Earthly rocks like basalts not only look like a meteorite, but they often exhibit magnetism which furthers confuses the matter. In such a case, the experience of the hunter comes into play. Suspect but promising specimens can be filed open with a diamond file to reveal a small window into the interior of the specimen. This window is then studied with a loupe or field microscope - the presence of chondrules or metal flecks is a giveaway that the specimen is meteoritic. Which is something else I should have mentioned earlier - CHONDRULES. Chondrules are another form of mineral that does not appear on Earth. Chondrules were formed under conditions not present on Earth at any time during it's history. To see tiny little perfect spheres of various minerals suspended in a surrounding matrix is "unearthly". To see chondrules, one must usually cut or file open the specimen - unless it's very weathered, in which case the matrix may be exposed and the chondrules readily visible. Chondrules range in size from several microns to several millimeters across and come in a variety of colors and compositions.

BTW, did you find the print out I enclosed in the box? It answers the "how do you know" question, but if it doesn't, then feel free to let me know - because I could use the feedback. You are the first person to read that brochure, and I want to know if it gets the definition across to someone with little or no meteorite experience.

I hope this helps.

The links Ed posted are great places to start as well.

Regards and clear skies,

MikeG

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Michael Gilmer - Member of the Meteoritical Society & Collector of Falling Stars.

Galactic Stone & Ironworks - Buy/Sell/Trade Meteorites, Moon Rocks, Mars Rocks, & Celestial Irons