[meteorite-list] Rusty rocks-- Lawrencite Disease, Trixie

[Mr EMan]

There is a name for this Rusty Rock condition which
veterans of collecting know as "Lawrencite" disease.
Lawrencite is the mineral Iron/Nickel Chloride
(Fe,Ni)Cl2.  In fact Lawrencite's type classification
location was a Georgia USA Meteorite.  "Drying out" a
meteorite isn't an complete answer because  Lawrencite
is a moisture attractant(deliquescencent) that
facilitates --in catalyst fashion, the rebinding of
free iron with water derived oxygen, creating rust and
Hydrochloric acid. The chlorine is never used up but
recycled so long as there is iron and water.
Elton

PS: Don't know about the electrical current issue
other than sounds like a plating problem

PPS: Congrats to the meteorite sniffing dog, Trixie do
tell us more!. Don't worry; she can't catch Lawrencite
disease.

>From Bill Cordua's
Site:<http://www.uwrf.edu/~wc01/SickMeteors.html>

Sick Meteorites

Meteorites have broken off asteroids, whirled through
space for billions of years, survived a fiery passage
through the earth's atmosphere and bashed into the
planet's surface. After this turbulent history, one
would not expect these meteorites would meet one of
their greatest danger residing in a cabinet in a
museum. Yet it is here that they "catch" the dreaded
"lawrencite disease". Once caught, the meteorite turns
rusty, exudes green or brown goo and eventually falls
to pieces. Only an air-tight sealing in dry nitrogen
gas seems to hold off final destruction. These
meteorites need to be on life support!

Of course "lawrencite disease" is not a biological
condition like human diseases and it is definitely not
catching! It is a kind of chemical weathering that
afflicts meteorites that contain the mineral
lawrencite. Lawrencite is iron chloride (FeCl2). It is
a soft green to brown hexagonal mineral that forms
small masses or coatings along the boundaries between
the iron-nickel alloy minerals (such as taenite and
kamacite) that make up the bulk of iron meteorites.
The taenite and kamacite are what show up as the
brightly shining tabular crystals seen on polished
iron meteorite surfaces. The lawrencite films along
the grain boundaries don't often show up on these
polished surfaces, at least not at first. They will
soon make their presence known as the meteorite is
exposed to air and water.

Lawrencite shows a property called "deliquescence".
This means it absorbs water from the air and
liquefies. The liquefaction produces the brown to
green gooey sludge which begins to form around the
shiny metallic alloys. This sludge consists of iron
oxides plus hydrochloric acid, which attacks the other
iron minerals, making more sludge and so forth.
Eventually the affected areas spread, wedge apart and
alter the other minerals and eventually reduce the
meteorite sample to a pile of rusty debris. There is
no cure - short of sealing the meteorite away.

A meteorite type called pallasite is particularly
vulnerable to this conditions. These meteorites
contain deep green clear olivine crystals set in a
matrix of nickel;-iron alloys. Slabbed and polished
samples of pallasites are beautiful and expensive.
However, if the lawrencite disease strikes, the sample
deteriorates rapidly, with the olivine crystals
falling out as the alloys rust away. Always look for
incipient rusty or gooey areas along grain boundaries
before buying one of these!

So it goes with meteorites foolish enough to leave the
safety of pure space for the impure chemical soup we
lovingly call our earth's environment.

- Dr. Bill Cordua, U. Wisconsin - River Falls

References:

Norton, O. Richard, 1994, Rocks from Space, Mountain
Publishing Co,, .

Palache, C., H. Berman and C. Frondell, 1951, Dana's
System of Mineralogy, 7th. edition, vol. I and II,
John Wiley Publishers, New York.




--- Steve Dunklee <sdunklee72520 at yahoo.com> wrote:

 On another
> note after playing fetch using nwa 869 meteorites
> for several months, my Lab Trixie has found her
> first meteorite, a small ordinary chondrite.
>   Best regards
>   Steve
> 
>