Manganiandrosite-(La)
Chemical formula: Mn<sup>2+</sup>La<sup>3+</sup>AlMn<sup>3+</sup>Mn<sup>2+</sup>(Si<sub>2</sub>O<sub>7</sub>)(SiO<sub>4</sub>)O(OH)
Manganiandrosite-(La) is an extremely rare mineral from the epidote group, characterized by its black color and unique chemical composition rich in manganese and lanthanum.
Description
## Characteristics Manganiandrosite-(La) is a complex silicate belonging to the epidote supergroup. It typically forms anhedral (irregular) to subhedral (poorly formed) prismatic crystals, which most often occur as granular aggregates. Its most characteristic visual feature is its black, opaque color. ## Physical Properties This mineral has a hardness of approximately 6 on the Mohs scale. It exhibits a submetallic luster and a significant density of about 4.18 g/cm³. It is brittle and opaque. ## Colors and Varieties The only known color of manganiandrosite-(La) is black. The streak of the mineral is reddish-brown. No color varieties or commercial varieties are known. ## History and Name The mineral was first described in 2003 by a team of mineralogists led by P. Bonazzi. Its name refers to its chemical composition – a high manganese content ("mangani") and a structural relationship with androsite-(La), with lanthanum ("La") as the dominant rare-earth element.
Diagnostic features
## Identification Identification in the field or based on visual characteristics is practically impossible. Key features include black color, high density, reddish-brown streak, and co-occurrence with other manganese minerals in a specific geological environment. Definitive identification requires advanced analytical techniques such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other black, dense minerals from the epidote supergroup, such as piemontite or allanite-(Ce), as well as other manganese oxides (e.g., braunite). Differentiation is only possible based on precise chemical analysis, which shows the dominance of lanthanum over other rare-earth elements and the specific roles of manganese in the structure. ## Crystal Forms It occurs as poorly formed, prismatic crystals, usually forming granular or massive aggregates.
Geological environment
## Genesis It forms under conditions of regional metamorphism in manganese-rich rocks, such as piemontite-braunite quartzitic schists. ## Mineral Associations In its type locality, it co-occurs with minerals such as braunite, piemontite, quartz, hematite, cryptomelane, ardennite-(As), and albite. ## Localities The only confirmed occurrence worldwide is the Varenche mine in the Aosta Valley, Italy.
Rarity
Extremely rare
Collector aspects
## Quality Criteria For such a rare mineral, occurring mainly as microscopic grains, the main criterion for value is the mere presence of an analytically confirmed specimen. Every crystal, even poorly formed, is valuable. Association with other rare minerals from this locality increases its value. ## Popular Localities The most (and only) prized specimens come from the type locality – the Varenche mine in Italy.
Care and storage
## Cleaning Due to its extreme rarity, utmost caution is advised. The safest way to remove dust is with a soft brush or a stream of compressed air. Washing in water is not recommended, and if necessary, only distilled water should be used, and the specimen should be thoroughly dried immediately. ## What to Avoid Ultrasonic cleaners, strong detergents, and all acids should be strictly avoided. The mineral's stability in sunlight and varying temperatures is not well-studied, so it is recommended to protect it from exposure to these factors. ## Storage Specimens, usually microscopic in size, should be stored in specialized, padded boxes (so-called "perky boxes"), away from dust and other reactive minerals.