Oxykinoshitalite

Chemical formula: BaMg<sub>2</sub>Ti<sup>4+</sup>O<sub>2</sub>(Si<sub>2</sub>Al<sub>2</sub>)O<sub>10</sub>

Oxykinoshitalite is a very rare mineral from the mica group, a brittle titanium-barium mica with a characteristic reddish-brown color.

## Characteristics Oxykinoshitalite is a mineral belonging to the mica group, specifically to the brittle mica subgroup. It forms tabular or platy crystals, often aggregated into small, radial clusters. Its most characteristic visual feature is its reddish-brown to dark brown color. As a member of the brittle micas, it is more fragile than common micas such as biotite or muscovite. ## Physical Properties This mineral is characterized by a hardness of 4.5 on the Mohs scale, making it relatively soft. The luster on cleavage surfaces is vitreous to pearly. It is a translucent mineral. Its density is approximately 3.55 g/cm³, which is a relatively high value for a silicate, resulting from the presence of barium and titanium in its structure. ## Colors and Varieties The observed colors of oxykinoshitalite are limited to shades of brown, most commonly reddish-brown and dark brown. No color or commercial varieties have been distinguished. ## History and Name Oxykinoshitalite was first described in 2000 by M. Bunno, T. Maruyama, and H. Sameshima. Its name refers to two characteristics: it is an oxygen-bearing (oxy-) analogue of kinoshitalite, and it is structurally related to it. The type mineral is kinoshitalite, in which a hydroxyl group (OH) is present in a specific structural position instead of oxygen. ## Applications Due to its extreme rarity, oxykinoshitalite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections of systematic and rare minerals.

Properties

Mohs hardness
4.5
Luster
Vitreous to pearly
Streak
Pale brown
Density
3.55
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include its micaceous habit (platy crystals, perfect cleavage in one direction), reddish-brown color, and relatively high density. However, the most important indicator is its specific occurrence environment and associated minerals. ## Distinguishing from Similar Minerals Oxykinoshitalite can be confused with other brown micas, such as biotite, phlogopite, or even kinoshitalite. Distinguishing it from biotite and phlogopite is possible based on its higher density and brittleness. Identification and differentiation from kinoshitalite require advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). In collecting practice, the main identification method is a confirmed locality of origin. ## Crystal Forms Crystals are thin to thick tabular with a pseudohexagonal outline. They usually occur as embedded flakes or small, rosette-like aggregates in the host rock.

Geological environment

## Genesis Oxykinoshitalite is a mineral formed under conditions of contact metamorphism. It forms at high temperatures and low pressures within metamorphosed manganese ore deposits. ## Mineral Associations This mineral co-occurs with other rare manganese and barium minerals. At the type locality, it was found in association with tamagawite, tephroite, celsian, diopside, and rhodochrosite. ## Localities The only confirmed and well-documented occurrence of oxykinoshitalite in the world is its type locality – the Noda-Tamagawa mine in Iwate Prefecture, Japan. This is a historic manganese ore mine, known for the occurrence of many rare mineral species.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those that contain well-formed, clearly visible crystals or aggregates with an intense, reddish-brown color. The rock matrix and the presence of rare associated minerals, such as tamagawite, are also of great importance. Due to its overall rarity, any authentic specimen is considered valuable. ## Popular Localities All collector specimens originate from a single location in the world: the Noda-Tamagawa mine in Japan. This mine is no longer active, which means that new material does not appear on the market, and the value of historical specimens increases.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used. Ultrasonic cleaners should be avoided, as they could cause delamination and damage to the crystals. ## What to Avoid The mineral is soft and has perfect cleavage, making it very susceptible to impact and scratching. It should be protected from contact with harder minerals. Contact with strong acids and other aggressive chemicals should be avoided. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent mechanical damage. Exposure to strong sunlight is not advisable, although the mineral is considered stable under typical conditions.

Sources

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