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Saving Private Iron, part one: Lawrencite Disease

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#1 lee14

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Posted 17 February 2024 - 12:41 PM

Lawrencite 'disease' refers to a series of chemical reactions involving ferrous chloride (FeCl2), ferric chloride (FeCl3), and hydrochloric acid (HCl). Ferrous Chloride is the mineral Lawrencite, which can be present in meteorites. Terrestrial chlorides, absorbed by prolonged contact with ground water that also transport salt (NaCl) into micro fissures and plate boundaries can also be a contributing factor. Ferrous chloride can react with atmospheric oxygen and water to produce ferric chloride and ferric hydroxide. Additional moisture can initiate a reaction that produces hydrochloric acid from the FECl3. The HCl will react with the surface iron, and/or penetrate microscopic boundaries between the crystal plates causing disintegration of the specimen. Lawrencite disease is distinguished from ordinary rust by the presence of yellowish-green-brown droplets at the surface of a whole specimen, or between the crystal plates on a sliced sample.

 

The image here is of a 755g Canyon Diablo that contains an area where this 'goo' is being exuded. It's the dark region occurring at a fissure crossing the center of the image. Although the piece was treated almost 20 years ago to remove any chlorides through chemical means, it seems that this particular area was resistant to penetration. The remaining surface is unblemished.

 

Lee

 

200.05-755g Canyon Diablo.jpg


Edited by lee14, 17 February 2024 - 12:46 PM.

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