Gadolinite-(Ce)

Chemical formula: Fe<sup>2+</sup>Be<sub>2</sub>Ce<sup>3+</sup><sub>2</sub>(SiO<sub>4</sub>)<sub>2</sub>O<sub>2</sub>

Gadolinite-(Ce) is a rare, black mineral of the gadolinite group, a cerium, beryllium, and iron silicate, characteristic of granitic pegmatites.

## Characteristics Gadolinite-(Ce) is a mineral belonging to the gadolinite group, in which cerium is the dominant rare-earth element in its composition. It typically occurs as embedded, anhedral masses or as prismatic, poorly formed crystals. Its color is most often black, less commonly brownish-black or greenish-black. This mineral is opaque, only slightly translucent on thin edges. ## Physical Properties The Mohs hardness of gadolinite-(Ce) is 6.5-7, making it relatively scratch-resistant. It exhibits a vitreous luster, which can transition to greasy or resinous on fracture surfaces. It is a brittle mineral, with a conchoidal to uneven fracture. Its density is significant, ranging from 4.2 to 4.7 g/cm³. Due to the frequent presence of radioactive elements such as thorium and uranium in its composition, gadolinite-(Ce) exhibits radioactivity. Prolonged radiation exposure leads to partial or complete destruction of its crystal lattice, i.e., metamictization. ## Colors and Varieties This mineral does not form colored or commercial varieties. Its color is uniform, usually black, brownish-black, or greenish-black. Classification within the gadolinite subgroup is based solely on the dominant rare-earth element in the chemical composition, which is indicated by an appropriate suffix, e.g., -(Ce) for cerium or -(Y) for yttrium. ## History and Name The name of the entire mineral group – gadolinite – honors the Finnish chemist and mineralogist Johan Gadolin, who first isolated yttrium oxide from a mineral sample found in Ytterby, Sweden. The suffix "-(Ce)" was added in accordance with IMA nomenclature to indicate that cerium dominates in this specific variety. The type locality for gadolinite-(Ce) is considered to be the Buer area in Norway. ## Applications Gadolinite-(Ce) has no direct industrial applications. However, it is of scientific interest as a mineral containing rare-earth elements. It is also valued by collectors specializing in pegmatite and rare-metal minerals.

Properties

Mohs hardness
6.5-7
Luster
Vitreous to greasy
Streak
Greenish-gray
Density
4.2-4.7
Cleavage
Poor
Fracture
Conchoidal to uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Features facilitating the identification of gadolinite-(Ce) include its black color, vitreous to greasy luster, conchoidal fracture, and high density. A key diagnostic feature is its radioactivity, which can be measured with a Geiger counter. Its occurrence in granitic pegmatites in association with other rare-earth minerals is also a strong indication. ## Distinguishing from Similar Minerals Gadolinite-(Ce) is visually almost identical to gadolinite-(Y) and allanite-(Ce). Definitive differentiation of these minerals requires advanced chemical analyses (e.g., EDS, WDS) to determine the dominant rare-earth element. It can also be confused with black tourmaline (schorl), hornblende, or some minerals from the pyrochlore group. However, tourmaline and hornblende are not radioactive and have significantly lower density. Minerals such as euxenite or samarskite, also black, radioactive, and occurring in pegmatites, usually have a stronger luster and a slightly different crystal habit. ## Crystal Forms Gadolinite-(Ce) crystallizes in the monoclinic system. It most often forms coarse-grained, prismatic crystals with poorly developed faces, deeply embedded in the host rock. More frequently, however, it is found in the form of irregular, compact aggregates and masses without visible crystal faces.

Geological environment

## Genesis Gadolinite-(Ce) is an igneous mineral, typical of the late stages of crystallization in granitic and syenitic pegmatites. It forms in an environment rich in rare-earth elements, beryllium, iron, and silica. ## Mineral Associations This mineral often co-occurs with other minerals characteristic of pegmatites, such as feldspars (albite, microcline), quartz, micas (biotite, muscovite), as well as other rare-earth minerals, e.g., allanite, monazite, xenotime, fergusonite, and zircon. ## Localities The most important and classic localities of gadolinite-(Ce) are in Norway (Buer in the Porsgrunn area – type locality) and Sweden (e.g., Ytterby, Bastnäs). It is also known from pegmatites in Russia (Kola Peninsula, Urals), and from the United States (e.g., pegmatites in Colorado and Texas).

Rarity

Rare

For collectors

## Quality Criteria The most highly valued by collectors are specimens with well-formed, sharp, and undamaged crystals. The size of the crystals and their placement on the rock matrix are also very important, especially in aesthetic contrast with lighter minerals such as quartz or feldspars. Specimens from classic, historical localities, e.g., in Scandinavia, fetch higher prices. ## Popular Localities Among the most sought-after are specimens from Norwegian and Swedish pegmatites, which are considered classic for this mineral. They constitute historical research material and an adornment for many systematic collections worldwide.

Care and storage

## Cleaning Gadolinite-(Ce) specimens should be cleaned very carefully, using a soft brush and distilled water to remove dust and loose contaminants. Ultrasonic cleaners are not recommended, as vibrations can cause cracking in brittle, especially metamict, specimens. ## What to Avoid The mineral is sensitive to strong acids. Due to its natural radioactivity, prolonged, direct contact should be avoided. It is recommended to wash hands after each contact with a specimen. Inhaling dust that might be generated during processing or mechanical cleaning should be avoided. ## Storage It is recommended to store gadolinite-(Ce) in separate, clearly labeled containers, away from areas of constant human presence (e.g., bedrooms or desks). It should be isolated from other minerals that may be sensitive to radiation (e.g., some varieties of quartz, fluorite) to prevent damage or discoloration.

External references

Sources

Read more