Roumaite

Chemical formula: (Nb₅+,Ti₄+)(Ca,Na,&#₉₇₄₄;)₃(Ca,REE)₄(Si₂O₇)₂(OH)F₃

Roumaite is an extremely rare mineral from the silicate and niobate group, discovered in Guinea, forming brownish-yellow, anhedral grains.

## Characteristics Roumaite is a very rare, complex silicate and niobate from the wöhlerite group, formally recognized as a new mineral species in 2021. It occurs as small, anhedral (irregularly formed) grains, reaching up to 1 mm in size. It is characterized by a brownish-yellow color and vitreous luster. It is a translucent mineral. ## Physical Properties The luster of roumaite is vitreous, and its streak is white. The mineral is translucent. Hardness and cleavage have not yet been determined. The density calculated based on chemical composition and unit cell parameters is 3.61 g/cm³. ## Colors and Varieties It is known exclusively in one color variant – brownish-yellow. No varieties have been distinguished. ## History and Name The mineral's name comes from its discovery location – Rouma Island, part of the Loos Archipelago off the coast of Guinea. It was approved by the International Mineralogical Association (IMA) in 2021 under number IMA2021-061. ## Applications Due to its extreme rarity, roumaite has no practical application. It is solely an object of scientific research and is of interest to specialized micromineral collectors.

Properties

Luster: Vitreous
Streak: White
Density: 3.61
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of roumaite based on visual characteristics is impossible. The mineral occurs as small, uncharacteristic grains. Positive identification requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) to determine chemical composition and X-ray diffraction (XRD) to confirm the crystal structure. ## Distinguishing from similar minerals Roumaite is very similar to other minerals from the wöhlerite group. Distinguishing it from, for example, wöhlerite, låvenite, or niocalatite is only possible based on precise chemical analysis, which will show the characteristic proportions of niobium, titanium, calcium, and rare earth elements for roumaite. ## Crystal forms To date, only anhedral (xenomorphic) grains up to 1 mm in size have been described. No well-formed crystals have been observed.

Geological environment

## Genesis Roumaite forms in the specific environment of nepheline syenite pegmatites. These are rare-element-rich igneous rocks that crystallize in the final stages of alkaline magma evolution. ## Mineral associations This mineral occurs in association with other rare alkaline minerals. At the type locality, its co-occurrence with aegirine, albite, nepheline, eudialyte-group minerals, rinkite, and villiaumite has been observed. ## Localities The only confirmed locality of roumaite in the world is its type locality – Rouma Island in the Loos Archipelago, Conakry region, Guinea.

Rarity

Extremely rare

For collectors

## Quality criteria For such a rare micromineral, traditional quality criteria such as color or clarity are not very significant. The highest value is placed on any well-documented specimen from the type locality, whose authenticity has been confirmed by analyses. The value of a specimen is enhanced by the presence of rare associated minerals on the same rock matrix. ## Popular localities Roumaite is known from only one location in the world (type locality), which is not a popular or easily accessible collecting site.

Care and storage

## Cleaning Due to its extreme rarity and lack of detailed research on chemical stability, it is recommended to avoid any wet cleaning. Any contaminants can only be removed with compressed air or a very soft brush. ## What to avoid Contact with acids and other chemicals should be strictly avoided. Ultrasonic cleaners should not be used. As a mineral with incompletely known characteristics, it should be protected from temperature fluctuations, prolonged exposure to sunlight, and moisture. ## Storage Roumaite specimens, typically microminerals, should be stored in specialized "micromount" boxes that protect them from mechanical damage, dust, and changes in environmental conditions.

Sources

IMA Mineral List (CNMNC)