Ferriperbøeite-(La)
Chemical formula: (CaLa<sup>3+</sup><sub>3</sub>)(Fe<sup>3+</sup>Al<sub>2</sub>Fe<sup>2+</sup>)[Si<sub>2</sub>O<sub>7</sub>][SiO<sub>4</sub>]<sub>3</sub>O(OH)<sub>2</sub>
Ferriperbøeite-(La) is an extremely rare mineral from the gatellite group, a complex silicate of calcium, lanthanum, and iron, found as black, resinous grains.
Description
## Characteristics Ferriperbøeite-(La) is a complex silicate belonging to the gatellite group within the epidote supergroup. It forms irregular, anhedral grains typically not exceeding 1-2 mm in size. Its characteristic features include a black color and a strong, resinous luster, which can transition to subadamantine. ## Physical Properties The mineral's hardness on the Mohs scale is approximately 6.5, placing it among relatively hard minerals. It is brittle, and its density is high, around 4.67 g/cm³. It is an opaque mineral. ## Colors and Varieties This mineral occurs exclusively in black. No color varieties or commercial forms are known. ## History and Name Ferriperbøeite-(La) was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2016. Its name refers to its chemical composition and structure. The "Ferri-" prefix indicates the dominance of ferric iron (Fe³⁺), "perbøeite" emphasizes its structural relationship with perbøeite-(Ce), and the "-(La)" suffix signifies that lanthanum is the dominant rare earth element in its composition. It was discovered in the Lovozero Massif on the Kola Peninsula in Russia.
Diagnostic features
## Identification Helpful identification features include: black color, resinous to subadamantine luster, high density, and a specific occurrence environment (hyperalkaline pegmatites). However, definitive identification is impossible without advanced analytical techniques, such as X-ray microanalysis (EDS/WDS) to determine chemical composition. ## Distinguishing from Similar Minerals Visually, it is indistinguishable from other black minerals of the epidote supergroup occurring in the same environment, such as ferriallanite-(La), perbøeite-(Ce), or gatellite-(Ce). Key differences lie in the proportions of rare earth elements (La vs Ce) and iron and aluminum, which require specialized research equipment. ## Crystal Forms Ferriperbøeite-(La) does not form well-developed crystals. It occurs exclusively as anhedral (irregular, lacking self-formed faces) grains and small aggregates thereof.
Geological environment
## Genesis This mineral crystallizes in the late stages of magma evolution in a unique geological environment: highly differentiated, hyperalkaline (agpaitic) nepheline syenite pegmatites. These rocks are extremely enriched in rare elements, including lanthanides. ## Mineral Associations It coexists with a rich assemblage of rare minerals typical of the Lovozero Massif. The most common associated minerals include aegirine, nepheline, sodalite, lorenzenite, lamprophyllite, eudialyte, and seidozerite. ## Localities The only confirmed locality for ferriperbøeite-(La) in the world (type locality) is the Seidozeritovoye No. 61 pegmatite vein on Mount Kedykverpakhk in the Lovozero Massif, Kola Peninsula, Murmansk Oblast, Russia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria As a "micromount" status mineral, its primary value is the mere presence of an analytically confirmed grain. Specimens are highly prized where the ferriperbøeite-(La) grain is clearly visible, exceeds 1 mm in size, and is embedded in a matrix with well-identified associated minerals. Luster and absence of mechanical damage also enhance the specimen's appeal. ## Popular Localities The only source of specimens is the type locality in the Lovozero Massif, Russia. Collector material is extremely difficult to obtain and appears on the market sporadically, mainly in specialized circles.
Care and storage
## Cleaning Due to the extreme rarity and small size of specimens, mechanical cleaning is highly risky. If necessary, a very soft brush can be used to remove loose dust. Ultrasonic cleaners and any chemical agents should be avoided. ## What to Avoid The mineral is potentially sensitive to strong acids. The presence of ferrous iron (Fe²⁺) theoretically poses a risk of slow oxidation in a humid environment. Avoid sudden temperature changes and prolonged exposure to moisture. ## Storage Ferriperbøeite-(La) specimens are typically micromounts. They should be stored in stable conditions, in a closed, padded "micromount" box, protected from dust, light, and moisture. Each specimen should have a precise label with a confirmed locality.