Lawrencite

Chemical formula: Fe²⁺Cl₂

Lawrencite is a rare iron(II) chloride found mainly in meteorites, which is highly hygroscopic and unstable in contact with moist air.

## Characteristics Lawrencite is a hydrated iron(II) chloride, known primarily for its extraterrestrial origin. It occurs almost exclusively in iron and stony-iron meteorites. Pure, unaltered lawrencite is white, but due to its extreme hygroscopicity, it reacts rapidly with atmospheric moisture, oxidizing and changing color to green, then brown. This process leads to its rapid decomposition and destruction of the meteorite structure in which it is found, a phenomenon known as "meteorite disease." ## Physical Properties This mineral is very soft and delicate. Its density is approximately 3.16 g/cm³. It is translucent. Due to its instability, observing its physical properties is difficult. ## Colors and Varieties Fresh, unaltered lawrencite is white. Under the influence of moisture and oxygen from the air, it quickly turns greenish, and eventually transforms into brown or reddish-brown oxidation products, such as akaganeite and goethite. ## History and Name The mineral's name honors American chemist John Lawrence Smith (1818-1883), who was a pioneer in studying the chemical composition of meteorites. The mineral was described in 1877 based on findings in the Tazewell meteorite, which fell in Claiborne County, Tennessee, USA. ## Uses Lawrencite has no industrial applications. Its significance is purely scientific, as an indicator of conditions prevailing in the parent bodies of meteorites. For meteorite collectors, it is a problematic mineral, causing the destruction of valuable specimens.

Properties

Luster
Resinous
Density
3.16
Cleavage
On {0001} ?
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification The presence of lawrencite in a meteorite is most often revealed by symptoms of its decomposition. "Sweating" droplets of a greenish or brownish, oily liquid (iron chloride solution) appear on the meteorite's surface, which over time crystallize as rusty efflorescences. This is a sure sign of its presence. ## Distinguishing from Similar Minerals Decomposition products of lawrencite, such as akaganeite, may resemble ordinary rust (goethite, lepidocrocite), but their appearance as "droplets" on a fresh meteorite cutting surface is very characteristic of lawrencite. ## Crystal Forms Lawrencite forms small, platy or flaky crystals. Most often, it occurs as fine grains, veins, or inclusions within the metallic mass (kamacite and taenite) of iron meteorites.

Geological environment

## Genesis Lawrencite is a primary mineral that formed in the parent bodies of asteroids under conditions of very low oxygen partial pressure and absence of water. It is a product of the reaction of iron with chlorine present in the primordial solar nebula. On Earth, its occurrence is limited to the interior of meteorites, which protected it from the terrestrial atmosphere. ## Mineral Associations It co-occurs with the main components of iron meteorites: kamacite and taenite. It is also accompanied by other accessory minerals found in meteorites, such as troilite, schreibersite, and graphite. ## Locations This mineral is found in many iron and stony-iron meteorites (pallasites and mesosiderites) worldwide. The type locality is the Tazewell meteorite (Tennessee, USA). Other known examples include the Nantan (China), Sikhote-Alin (Russia), Canyon Diablo (USA), and Muonionalusta (Sweden) meteorites.

Rarity

Rare

For collectors

## Quality Criteria Lawrencite itself is not a collectible item due to its instability. Its presence in a meteorite is considered a serious defect that threatens the stability of the specimen. The phenomenon of lawrencite decomposition, although destructive, is scientifically interesting and is documented by advanced collectors and researchers. ## Popular Localities Lawrencite itself is not collected, but rather meteorites in which it may occur. Meteorites from desert finds (e.g., from Northwest Africa) or ice finds (Antarctica) often show strong signs of its decomposition due to prolonged contact with moisture.

Care and storage

## Cleaning Lawrencite is not cleaned in the traditional way. Any contact with water, alcohol, or other liquids leads to its immediate decomposition. Specimens (meteorites) containing lawrencite require specialized conservation under anhydrous conditions. ## What to Avoid Contact with moisture and water must be strictly avoided. Even moisture in the air is destructive to it. Storage under normal atmospheric conditions leads to its rapid oxidation and disintegration, which also destroys the surrounding meteoritic material. ## Storage Specimens containing lawrencite must be stored under completely anhydrous conditions. The best solution is to keep them in sealed containers with a desiccant (e.g., silica gel) or in an inert gas atmosphere (e.g., nitrogen or argon). Some collections store such specimens in anhydrous liquids, such as paraffin oil.

External references

Sources

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