Matsubaraite
Chemical formula: Sr<sub>4</sub>Ti<sup>4+</sup><sub>5</sub>O<sub>8</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>
A very rare strontium titanium silicate, forming small, black prismatic crystals.
Description
## Characteristics Matsubaraite is a sorosilicate mineral distinguished by its complex chemical composition containing strontium and titanium. It occurs as small, prismatic crystals, rarely exceeding a few millimeters in length. These crystals often form radial or fan-shaped aggregates. The mineral is opaque and ranges in color from black to brownish-black. ## Physical Properties Matsubaraite has a Mohs hardness of 5.5 to 6, placing it on par with orthoclase. It exhibits a submetallic luster, and its density, calculated from its chemical composition and crystal structure, is approximately 4.31 g/cm³. It shows good cleavage in one direction, and its fracture is uneven. ## Colors and Varieties This mineral is uniform in color, occurring exclusively in shades of black and dark brown. No color varieties or commercial forms are known. ## History and Name The name matsubaraite was given in honor of Dr. Satoshi Matsubara (1952–2016), a Japanese mineralogist from the National Museum of Nature and Science, Tokyo, in recognition of his contributions to the study of minerals from Japan, including those from skarns. The mineral was officially approved by the International Mineralogical Association (IMA) in 1996. ## Uses Due to its extreme rarity and occurrence only as microscopic crystals, matsubaraite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections of rare minerals and micromounts.
Diagnostic features
## Identification Field identification of matsubaraite is practically impossible. In a collection, it can be preliminarily recognized by its black color, submetallic luster, prismatic crystal habit, and radial aggregates. However, its occurrence environment (skarn) and associated minerals are key. Definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) and chemical composition analysis (EDS/WDS). ## Differentiation from Similar Minerals Matsubaraite can be confused with other black, titanium-bearing minerals found in similar environments, such as ilmenite or some pyroxenes. It is distinguished from them by its specific crystal habit, often in radial aggregates, and its unique chemical composition, rich in strontium, which is a feature impossible to determine without specialized equipment. ## Crystal Forms Crystals are elongated, prismatic. They most often form divergent, radial, or fan-shaped aggregates, growing from a single point.
Geological environment
## Genesis Matsubaraite is a mineral formed under conditions of high-temperature contact metamorphism. Its formation is associated with skarns, which are rocks formed at the contact of a magmatic intrusion (in this case, granodiorite) with carbonate rocks (limestones). ## Mineral Associations This mineral occurs in association with other minerals typical of skarns, such as gehlenite, vesuvianite, wollastonite, cuspidine, calcite, as well as rarer minerals like rankinite or biraite-(Ce). Co-occurrence with these minerals is an important diagnostic clue. ## Localities The sole and classic occurrence (type locality) of matsubaraite is the Fuka mine in Okayama Prefecture, Japan. This is a globally renowned locality for many rare skarn minerals.
Rarity
Very rare
Collector aspects
## Quality Criteria For such a rare mineral as matsubaraite, the primary criterion for value is its mere presence. Specimens with well-formed, sharp, and undamaged crystals, even if microscopic in size, are most highly prized. The formation of aesthetically pleasing, radial aggregates by the crystals enhances their attractiveness. Association with other rare minerals from the same locality is also important. ## Popular Localities The only source of collectible specimens is the type locality – the Fuka mine in Japan. Specimens from this location are highly sought after by specialized collectors of rare minerals and micromounts.
Care and storage
## Cleaning Specimens should only be cleaned using a soft brush to remove dust. For more stubborn dirt, compressed air (from a safe distance) or, as a last resort, distilled water and a very soft brush can be used. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is sensitive to strong acids. Contact with household and laboratory chemicals should be avoided. Due to its cleavage and moderate hardness, it should be protected from impacts, scratching, and vibrations. ## Storage The safest form of storage is a specialized "micromount" box, which protects delicate crystals from mechanical damage and dust. Exposure to extreme temperature changes should be avoided.