Gorceixite

Chemical formula: BaAl₃(PO₄)(PO₃OH)(OH)₆

Gorceixite is a hydrated barium aluminum phosphate, most commonly forming spherical aggregates or massive occurrences with a waxy luster.

## Characteristics Gorceixite is a mineral from the plumbogummite group, belonging to the phosphate class. It rarely forms visible crystals, which take the form of pseudocubic or rhombohedral tablets. Most often, it occurs as radial or spherical aggregates, granular, reniform masses, as well as concretions and nodules. It can also be found as earthy or compact masses. Its appearance is usually inconspicuous, and specimens with well-formed crystals are rare. ## Physical Properties This mineral is characterized by a hardness of 4.5 on the Mohs scale. It has a waxy, resinous luster, and in the case of earthy forms, a dull luster. It is translucent to opaque. Its density ranges from 3.08 to 3.31 g/cm³. ## Colors and Varieties Gorceixite occurs in various colors; most often it is colorless, white, gray, yellowish, greenish, or brown. Some specimens may exhibit weak, bluish-white fluorescence under ultraviolet light. No named varieties of this mineral are distinguished. ## History and Name The mineral's name comes from Claude-Henri Gorceix (1842-1919), a French mining engineer and director of the School of Mines in Ouro Preto, Brazil, who was the first to study the diamond deposits where this mineral was found. The mineral was first described by E. Hussak in 1906 based on material from the Abaeté River in Minas Gerais, Brazil. ## Uses Gorceixite has no significant industrial application. It is primarily of interest to collectors specializing in rare minerals and to scientists studying weathering processes and the genesis of phosphate and diamond-bearing deposits.

Properties

Mohs hardness
6
Color
White, colorless, green or brown, may be mottled; colourless in transmitted light..
Luster
Resinous
Streak
White
Density
3.036
Cleavage
Good on {0001}
Fracture
Conchoidal,Sub-Conchoidal
Transparency
Transparent,Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Gorceixite is most often identified by its mode of occurrence – spherical or reniform aggregates with a radial internal structure. Its characteristic waxy or resinous luster is also distinctive. In rare cases, when it forms crystals, they have the shape of pseudocubic rhombohedra. It is relatively soft (hardness 4.5). ## Distinguishing from Similar Minerals Gorceixite is often confused with other minerals from the plumbogummite group (e.g., plumbogummite, crandallite, goyazite), from which differentiation without advanced chemical analyses (EDS, XRD) is practically impossible. It may resemble some forms of chalcedony or variscite, but differs from them in hardness and density. ## Crystal Forms Well-formed crystals are rare and usually microscopic in size. They take the form of tabular, pseudocubic rhombohedra. The predominant forms of occurrence are radially fibrous aggregates, spherical aggregates (spherulites), concretions, granular masses, and earthy masses.

Geological environment

## Genesis Gorceixite is a secondary mineral. It forms in weathering zones of phosphorus-rich rocks, especially carbonatites and pegmatites. It also forms as a result of low-temperature hydrothermal processes. It is also a residual mineral, found in alluvial (river) sediments, where it concentrates due to its chemical resistance, often in association with diamonds. ## Mineral Associations It co-occurs with minerals such as diamond, quartz, kaolinite, crandallite, goyazite, florencite, monazite, rutile, zircon, and in carbonatites with barite, calcite, and apatite. ## Localities The most important gorceixite localities worldwide are the diamond deposits in Minas Gerais, Brazil (especially in the Diamantina region and the Abaeté River – the type locality). It also occurs in the Catalão region of Brazil in carbonatites. It is also known from Arkansas (USA), Germany (Bavaria), Russia (Kola Peninsula), the Democratic Republic of Congo, and Australia.

Rarity

Not very common

For collectors

## Quality Criteria For collectors, the most desirable specimens are those with well-formed, even if microscopic, crystals with a distinct rhombohedral shape. Aesthetic, spherical aggregates with intense color and good luster are also highly valued. The attractiveness of a specimen is enhanced by its association with other minerals, especially diamond, although such finds are extremely rare. ## Popular Localities The most classic and valued specimens by collectors come from historical localities in Brazil, in the state of Minas Gerais. Specimens from carbonatites, e.g., from Catalão in Brazil or from the Kola Peninsula in Russia, are also sought after by specialists.

Care and storage

## Cleaning Gorceixite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, avoiding prolonged soaking. Ultrasonic cleaners should not be used, as they can damage delicate aggregates. ## What to Avoid The mineral is sensitive to strong acids, which can damage it. Contact with household and laboratory chemicals should be avoided. It should not be subjected to sudden temperature changes. ## Storage Collector's specimens of gorceixite, especially those with delicate structures (radial aggregates, earthy forms), are best stored in sealed boxes or display cases to protect them from dust and mechanical damage. It does not require special protection from light.

External references

Sources

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