[meteorite-list] Weathering Grades

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:59 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86904EE5910_at_US-Torrance.mail.saic.com>

Hi Rafael,

> I heard that Weathering Grade is explained in the New book of Cambridge
> Encyclopedia of meteorites, but I dont have it :(, and no one in my
> city that I know have it. Thanks list...

Perhaps the attached reposted message from Piper will help you:

--Rob

- - - -

The meteorite weathering grade scale W0-W6 now commonly used was first
described by F. Wlotzka of the Department of Cosmochemistry at the Max
Planck Institute in Mainz, Germany in a short article 'A Weathering Scale
for Common Chondrites' published in Meteoritics, July 1993. This article
is available online in NASA's ADS database:

http://adsabs.harvard.edu/abstract_service.html

Here is Wlotzka's short description of the weathering grades:

W0 -no visible oxidation of metal or sulfide but a limonitic staining may
be noticeable in transmitted light. Fresh falls are usually of this grade,
although some are already W1.
W1 - minor oxide rims around metal and troilite and minor oxide veins.
W2 - moderate oxidation of metal, about 20-60% being affected.
W3 - heavy oxidation of metal and troilite, 60-95% being replaced.
W4 - complete (>95%) oxidation of metal and troilite, but no alteration of
silicates.
W5 - beginning alteration of mafic silicates, mainly along cracks.
W6 - massive replacement of silicates by clay minerals and oxides.

Best wishes to all,

Piper Hollier
Amsterdam NL
Received on Wed 07 Jan 2004 02:50:57 PM PST