Gatedalite
Chemical formula: Zr<sup>4+</sup>Mn<sup>2+</sup><sub>2</sub>Mn<sup>3+</sup><sub>4</sub>SiO<sub>12</sub>
Gatedalite is an extremely rare, black mineral of the braunite group, known exclusively from a single locality in Sweden.
Description
## Characteristics Gatedalite is a mineral of the braunite group, a zirconium and manganese silicate with the formula ZrMn²⁺₂Mn³⁺₄SiO₁₂. It occurs as very small, anhedral (irregular) grains up to 0.2 mm in size. It is black and opaque, with a submetallic luster. It is typically strongly intergrown with other manganese minerals, forming fine-grained aggregates. ## Physical Properties The Mohs hardness is approximately 6.5. The mineral is characterized by a submetallic luster and is opaque. The density calculated from the chemical composition and unit cell parameters is 4.83 g/cm³. ## Colors and Varieties It is known exclusively in black color. No varieties have been distinguished. ## History and Name The mineral was approved by the IMA in 2010. Its name comes from the discovery locality - the Gatedalen iron and manganese deposit in the Jämtland region of Sweden. It was described by the Swedish mineralogist Dan Holtstam and his colleagues in 2011. ## Uses Due to its extreme rarity and occurrence as microscopic grains, gatedalite has no practical application. It is solely an object of scientific and collecting interest within systematic collections.
Diagnostic features
## Identification Identification of gatedalite is impossible without advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD). In a macroscopic sample, it is indistinguishable from other black manganese oxides. Characteristic features in laboratory studies are: black color, submetallic luster, high hardness, and unique chemical composition with the presence of zirconium. ## Distinguishing from Similar Minerals It can be easily confused with braunite, hollandite, and hematite, with which it co-occurs. Braunite is visually very similar but does not contain zirconium. Distinguishing it from these minerals in field conditions or based on visual characteristics is impractical. ## Crystal Forms It occurs exclusively as anhedral, irregular grains of submillimeter size, most often embedded in the rock matrix or other minerals.
Geological environment
## Genesis Gatedalite forms under hydrothermal conditions. It was found in mineralized fissures cutting Ordovician limestones. Its formation is associated with low-temperature metamorphism or hydrothermal processes that led to the concentration of manganese and iron. ## Mineral Associations It most commonly co-occurs with braunite, hematite, hollandite, calcite, and quartz. ## Localities The only confirmed occurrence in the world is its type locality: the Fe-Mn deposit Gatedalen, Brunflo, Östersund, Jämtland, Sweden.
Rarity
Extremely rare
Collector aspects
## Quality Criteria For such a rare micromineral, the main criterion for value is confirmation of its identity by chemical analysis. The attractiveness of a specimen is enhanced by the abundance (quantity and size of gatedalite grains on the sample) and clear associations with other minerals. ## Popular Localities The only source of specimens is the type locality in Sweden. Material from this location is extremely difficult to obtain.
Care and storage
## Cleaning Specimens containing gatedalite are usually microminerals. Cleaning, if necessary at all, should be limited to gently removing dust with a soft brush or a photographic air blower. Avoid water and any chemical agents. ## What to Avoid Ultrasonic cleaners, strong acids and bases, and sudden temperature changes should be absolutely avoided. The mineral is stable under normal conditions, but its reaction to chemicals is not fully understood. ## Storage Specimens should be stored under stable room conditions, away from dust and moisture. The best way to store them is in "micromount" boxes, which protect delicate samples from mechanical damage.