Kosmochlor

Chemical formula: NaCr<sup>3+</sup>Si<sub>2</sub>O<sub>6</sub>

Cosmochlore is a rare, emerald-green sodium-chromium pyroxene, found mainly in iron meteorites and as a key component of the ornamental rock maw-sit-sit.

## Characteristics Cosmochlore is a mineral from the pyroxene group, being the chromium analogue of jadeite. Its name, derived from Greek, accurately reflects its nature - "cosmic green". It most often forms fine-grained, compact aggregates or irregular grains, strongly intergrown in the matrix of iron meteorites or in metamorphic rocks. Well-formed crystals are rarely observed. A distinguishing feature of cosmochlore is its intense, emerald or bright green color, which is due to its high chromium content. ## Physical properties This mineral is characterized by a hardness of 6 on the Mohs scale, making it relatively scratch-resistant. It has a vitreous luster, and its density ranges from 3.56-3.78 g/cm³, being noticeably higher than the density of visually similar minerals. It is translucent, and in thicker fragments or compact aggregates, it becomes opaque. ## Colors and varieties The dominant and essentially only color of cosmochlore is intense green, from emerald to dark green, almost black. No color varieties are distinguished, however, it is a key component of the rare ornamental rock known commercially as **maw-sit-sit**. This rock, originating from Myanmar, is a mixture of cosmochlore, jadeite, chromite, and other minerals, valued in jewelry for its unique, green-black pattern. ## History and name The mineral's name comes from the Greek words *kosmos* (space, universe) and *chloros* (green), referring to its original, extraterrestrial origin and characteristic color. It was first scientifically described in 1897 by Hugo Laspeyres, who identified it in samples of the Toluca iron meteorite, found in Mexico. ## Applications Due to its rarity, cosmochlore is primarily of scientific and collector's interest. It has no industrial applications. However, as a main component of maw-sit-sit rock, it is used as a gemological and ornamental material for making jewelry and small decorative objects.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.56-3.78
Cleavage
Good on {110}
Fracture
Conchoidal to uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification The most important diagnostic feature of cosmochlore is its intense, emerald-green color combined with relatively high hardness (6 on the Mohs scale) and high density. The context of its occurrence is also crucial - its presence in iron meteorites or in specific, high-pressure metamorphic rocks (like maw-sit-sit). ## Distinguishing from similar minerals Cosmochlore is sometimes confused with other green minerals: - **Jadeite**: Very similar, often co-occurs. Cosmochlore usually has a more intense, "chromian" green, higher density, and slightly different optical properties. Definitive differentiation requires advanced analysis. - **Uvarovite (garnet)**: Has a similar, chromian color, but is significantly harder (7.5-8) and crystallizes in the isometric system, most often forming small, shiny crystals as coatings, rather than compact aggregates. - **Chromian diopside**: This is also a green pyroxene, but it has a lower refractive index and lower density. Its shade of green is often slightly different. ## Crystal forms Cosmochlore most often occurs as anhedral (irregular) grains or forms massive, fine-grained aggregates. Well-formed, single crystals with a prismatic or tabular habit are extremely rare and found only as microscopic inclusions.

Geological environment

## Genesis Cosmochlore forms under specific conditions. Its primary environment of formation is iron meteorites, where it crystallizes under high pressure and low oxygen fugacity, often within graphite-troilite nodules. On Earth, its genesis is associated with high-pressure metamorphic processes occurring in subduction zones. It forms in rocks rich in sodium and chromium, such as jadeitites. ## Mineral associations Meteoritic occurrences: troilite, daubréelite, krinovite, chromite, graphite, metallic nickel and iron. Terrestrial occurrences (in maw-sit-sit type rocks): jadeite, eckermannite, arfvedsonite, chromite, natrolite. ## Localities The most important cosmochlore localities are associated with meteorites. It has been found, among others, in the Toluca and Coahuila meteorites (Mexico), Canyon Diablo (USA), and Morasko (Poland). The most famous terrestrial occurrence is the Tawmaw region in Myanmar (Burma), where it is the main component of maw-sit-sit rock. Other confirmed, though much rarer, localities are in Italy and Russia.

Rarity

Very rare

For collectors

## Quality criteria The collector's value of cosmochlore depends on its origin and form. For meteoritic specimens, polished slices showing rich, intensely green aggregates of the mineral contrasting with the metallic matrix are most prized. The higher the concentration and the more vibrant the color of the cosmochlore, the higher the value of the specimen. For terrestrial material, mainly maw-sit-sit rock, the key factors are the quality of the color, its saturation, and the attractive pattern created by black veins and spots. Pure, monomineralic aggregates of cosmochlore are exceptionally rare and fetch very high prices. ## Popular localities For collectors of extraterrestrial minerals, specimens from classic meteoritic localities, such as Toluca in Mexico, are most sought after. For enthusiasts of ornamental stones and gemology, material from Tawmaw in Myanmar is absolutely number one.

Care and storage

## Cleaning Cosmochlore specimens can be safely cleaned with lukewarm water, mild soap, and a soft brush. After washing, they should be thoroughly rinsed with clean water (preferably distilled) and left to air dry completely or gently dried with a soft cloth. Ultrasonic and steam cleaners are not recommended. ## What to avoid This mineral is sensitive to strong acids and other aggressive chemicals. Avoid sudden temperature changes, which can lead to internal fractures. Despite a hardness of 6, it should be protected from contact with harder minerals (e.g., quartz, topaz) to prevent scratches. ## Storage Collector's specimens of cosmochlore, especially those in a meteorite matrix, are best stored in stable conditions, in separate boxes or display cases lined with soft material. Protect from dust and moisture, especially in the case of meteoritic specimens, which may contain unstable minerals prone to corrosion.

External references

Sources

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