Maruyamaite

Chemical formula: K(MgAl₂)(Al₅Mg)(BO₃)₃(Si₆O₁₈)(OH)₃O

Maruyamaite is a potassium-magnesium tourmaline, characterized by extremely high hardness, close to that of diamond.

## Characteristics Maruyamaite is a mineral from the tourmaline group, being its potassium and magnesium end-member. It is one of the hardest known minerals on Earth. Its crystals are usually very small, reaching sizes up to several tens of micrometers, which makes them visible only under a microscope. It occurs as hexagonal, prismatic crystals embedded in the host rock. ## Physical Properties This mineral is characterized by extreme hardness, ranging from 9-10 on the Mohs scale, placing it just below diamond. It has a vitreous luster and is transparent to translucent. Its density is approximately 3.02 g/cm³. ## Colors and Varieties Observed maruyamaite crystals are colorless. Due to its rarity and microscopic size, no color or commercial varieties have been distinguished. ## History and Name Maruyamaite was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2013. Its name honors Yoshihiro Maruyama, a Japanese geologist who made significant contributions to research on ultrahigh-pressure metamorphism. The mineral was discovered in the Kokchetav subduction zone in northern Kazakhstan. ## Applications Due to its extreme rarity and microscopic size, maruyamaite has no industrial or commercial applications. Its significance is purely scientific, providing valuable information about conditions deep within the Earth's mantle.

Properties

Mohs hardness: 9-10
Luster: Vitreous
Streak: White
Density: 3.02
Cleavage: None
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of maruyamaite is impossible with the naked eye and requires advanced laboratory techniques, such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD). It occurs as microscopic, hexagonal crystals in a characteristic geological environment. ## Distinguishing from Similar Minerals Under the microscope, it can be confused with other minerals from the tourmaline group. Definitive distinction requires chemical composition analysis, especially to confirm the dominance of potassium at the X site. From diamond, with which it coexists, it is distinguished by crystal form and chemical composition. ## Crystal Forms It forms exclusively microscopic, hexagonal (trigonal) prismatic crystals, usually not exceeding 20-30 micrometers in length.

Geological environment

## Genesis Maruyamaite forms under ultrahigh-pressure (UHP) metamorphic conditions, at pressures exceeding 4 GPa and temperatures ranging from 800-950°C. Such conditions correspond to depths of over 120 km in the Earth's mantle. It forms in carbonate-silicate rocks and gneisses that have undergone deep subduction. ## Mineral Associations This mineral coexists with other indicator minerals for UHP conditions, such as microdiamonds, coesite, garnet (pyrope), kyanite, jadeite, dolomite, potassic phlogopite, and carbonates (magnesite, aragonite). ## Localities The only confirmed locality of maruyamaite in the world is the Kokchetav Massif in northern Kazakhstan. This is a classic locality for research on ultrahigh-pressure metamorphism.

Rarity

Extremely rare

For collectors

## Quality Criteria Maruyamaite is not a collector's mineral in the traditional sense. Its value is purely scientific. Specimens are rock fragments (microgneisses, carbonate-silicate rocks) with analytically confirmed presence of maruyamaite microcrystals. The most valuable are research samples with well-documented locality and compositional analysis. ## Popular Localities The only source of material for research is the Kokchetav Massif in Kazakhstan. Specimens from this locality, found in university collections and research institutions, are extremely valuable for science.

Care and storage

## Cleaning Due to the microscopic size of the crystals and their occurrence exclusively within the host rock, individual crystals are not subject to cleaning. Rock specimens containing maruyamaite can be cleaned with a soft, dry brush to remove dust. ## What to Avoid Avoid using any chemical agents, ultrasonics, or sudden temperature changes, which could damage the host rock and delicate mineral associations. Despite its high hardness, the mineral is brittle. ## Storage Specimens should be stored in stable conditions, away from dust, moisture, and direct sunlight. It is best to store them in collector's boxes or display cases to minimize the risk of mechanical damage.

Sources

IMA Mineral List (CNMNC)