Mottanaite-(Ce)

Chemical formula: Ca<sub>4</sub>Ce<sup>3+</sup><sub>2</sub>Al(Be<sub>1.5</sub>&#9744;<sub>0.5</sub>)[B<sub>4</sub>Si<sub>4</sub>O<sub>22</sub>]O<sub>2</sub>

Mottanaite-(Ce) is a rare mineral from the hellandite group, found as small, brown crystals in miarolitic volcanic cavities.

## Characteristics Mottanaite-(Ce) is a mineral from the hellandite group, belonging to the silicates. It forms elongated, prismatic crystals that usually do not exceed 1-2 mm in length. It most often occurs as radial aggregates or single, well-formed crystals grown on other minerals within rock cavities. ## Physical properties Mottanaite-(Ce) crystals are characterized by a vitreous luster. They are brittle, and their Mohs hardness is approximately 6. The mineral is transparent to translucent. ## Colors and varieties The dominant color is brown, often with a reddish or orange tint. Some crystals may be lighter, up to yellowish-brown. No varieties have been distinguished. ## History and name The mineral's name comes from its discovery locality in 2001 – a granite quarry in Mottana, in the municipality of Novate Mezzola, Lombardy, Italy. The "-(Ce)" suffix in the name indicates cerium as the dominant rare earth element in its structure. The mineral was officially approved by the International Mineralogical Association (IMA) in 2003. ## Applications Due to its rarity and small crystal size, mottanaite-(Ce) has no practical applications. It is solely an object of interest for collectors specializing in rare minerals and a subject of scientific research.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.81
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying mottanaite-(Ce) in collector's conditions is difficult and usually relies on analyzing the locality and associated minerals. Characteristic features include small, brown, prismatic crystals with a vitreous luster, forming radial aggregates in cavities of granitic rocks. Definitive identification requires advanced analytical methods, such as Raman spectroscopy or EDS analysis. ## Distinguishing from similar minerals It can be confused with other minerals from the hellandite group or tourmalines (e.g., dravite), with which it often co-occurs. Distinguishing them based on visual characteristics is practically impossible without specialized equipment. Knowledge of the mineralogy of the given locality is crucial here. ## Crystal forms Crystals are strongly elongated, prismatic, with a cross-section similar to a rectangle. They usually form fan-shaped or radial aggregates; less commonly, they occur as single, overgrown crystals.

Geological environment

## Genesis Mottanaite-(Ce) is a hydrothermal mineral. It crystallizes in the late stage of granite pegmatite evolution, within miarolitic cavities (pockets), under conditions enriched in elements such as boron, beryllium, and rare earth elements (mainly cerium). ## Mineral associations It most often co-occurs with albite, microcline, quartz, schorl (black tourmaline), stilbite, beryl, as well as other rare minerals such as hellandite-(Y) or gadolinite-(Y). ## Localities The most important and type locality (località typica) is the granite quarry in Mottana, in the Val Codera valley, Lombardy, Italy. This is the only confirmed and well-documented locality for this mineral in the world.

Rarity

Very rare

For collectors

## Quality criteria The quality of a specimen is assessed primarily based on the size and form of the crystals and their aggregates. Most valued are specimens with distinct, well-formed, radial aggregates of intense brown color, contrasting with the light background of the host rock (most often white albite). The presence of associated minerals, which confirm the specimen's origin, is also important. ## Popular localities The only source of collector specimens is the type locality – the Mottana quarry in Italy. All specimens available on the market come from this single location.

Care and storage

## Cleaning Extreme caution is recommended. Specimens should only be cleaned with compressed air to remove dust. The use of water, and especially ultrasonic cleaners, is highly risky due to the brittleness and small size of the crystals, which may be embedded in a delicate matrix. ## What to avoid Avoid contact with chemicals, acids, and detergents. Due to its brittleness, specimens must be protected from impacts, vibrations, and sudden temperature changes. ## Storage The safest storage method is to keep the mineral in its original, sealed collector's box (e.g., "micromount" type), lined with soft foam. Protect from dust and direct sunlight.

Sources

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