Mariinskite

Chemical formula: Cr<sup>3+</sup><sub>2</sub>BeO<sub>4</sub>

Mariinskite is an extremely rare chromium chrysoberyl, a natural analogue of alexandrite, distinguished by its intense green color.

## Characteristics Mariinskite is a very rare mineral from the oxide group, being a chromium analogue of chrysoberyl. It forms small, tabular or prismatic crystals, usually with a hexagonal outline, often exhibiting twinning. Its most characteristic feature is an intense, emerald-green color, resulting from a high chromium content. It is a natural counterpart of synthetic alexandrite grown by the flux method. ## Physical Properties This mineral is characterized by very high hardness, reaching 8.5 on the Mohs scale, which is typical for the chrysoberyl group. It has a vitreous luster and is transparent to translucent. Its density is relatively high, approximately 4.11 g/cm³. ## Colors and Varieties Mariinskite occurs in a uniform, intense, emerald-green color. It does not exhibit the color-change effect (alexandrite effect), which is characteristic of some chrysoberyl varieties. No varieties of mariinskite are distinguished. ## History and Name The mineral's name comes from the Mariinskoye deposit in the Urals, Russia, where it was first identified. It was officially recognized by the International Mineralogical Association (IMA) in 2011. The discovery was a result of research on material from a historic emerald and alexandrite deposit. ## Uses Due to its extreme rarity, small crystal sizes, and scientific significance, mariinskite is exclusively an object of collector's and scientific interest. It has no industrial or jewelry applications.

Properties

Mohs hardness
8.5
Luster
Vitreous
Streak
White
Density
4.11
Cleavage
Good on {011}, imperfect on {010}
Fracture
Conchoidal to uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features of mariinskite are its unique, intensely green color, very high hardness (8.5), and characteristic, hexagonally outlined, tabular crystals. Its origin is also an important indicator – almost exclusively from the Mariinskoye deposit in the Urals. ## Distinguishing from Similar Minerals Mariinskite can be confused with other green minerals of high hardness. It differs from emerald (a variety of beryl) by its higher hardness and different crystal habit. It differs from alexandrite (a variety of chrysoberyl) by the absence of the color-change effect. Chromian diopside and uvarovite are significantly softer. Final confirmation requires advanced analytical methods. ## Crystal Forms Mariinskite forms small, short, prismatic or tabular crystals, often with a pseudohexagonal habit. Twinning, including cyclic twinning forming six-rayed star-like shapes, is common.

Geological environment

## Genesis Mariinskite forms in metamorphic rocks – phlogopite schists that have undergone metasomatism under the influence of beryllium- and chromium-rich fluids. Its crystallization is associated with the interaction between ultramafic rocks (chromium source) and pegmatites or other beryllium-rich rocks. ## Mineral Associations This mineral co-occurs with chrysoberyl (including alexandrite), emerald, phenakite, phlogopite, plagioclase, and amphiboles. ## Localities The only confirmed and type locality for mariinskite in the world is the Mariinskoye (Malyshevskoye) deposit in the Middle Urals region of Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized mariinskite specimens are those with well-formed, sharp crystals of intense, emerald-green color and good transparency. Characteristic twinning is also highly valued. Due to its rarity, every authentic specimen, even a small one, has significant collector's value. ## Popular Localities The only source of collector specimens is the historic Mariinskoye deposit in the Urals, Russia. Material from this locality is extremely difficult to acquire and represents a crowning achievement for advanced systematic collections or those specializing in gem minerals.

Care and storage

## Cleaning Cleaning with lukewarm water using a very soft brush is recommended. Ultrasonic cleaners can be used, but with great caution. Strong detergents should be avoided. ## What to Avoid The mineral is very hard and chemically stable, but contact with hydrofluoric acid should be avoided. Despite its high hardness, specimens can be brittle, so they should be protected from impacts and sudden temperature changes. ## Storage Mariinskite specimens, being extremely rare and valuable, should be stored in separate, padded display boxes to prevent scratching by other minerals (although it is very hard itself) and to protect against mechanical damage. It should be protected from dust.

Sources

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