Silicocarnotite

Chemical formula: Ca<sub>5</sub>(PO<sub>4</sub>)<sub>2</sub>(SiO<sub>4</sub>)

Silicocarnotite is a rare calcium phosphate from the apatite group, found as microscopic grains in metamorphic rocks and some slags.

## Characteristics Silicocarnotite is a phosphate mineral belonging to the apatite group. It occurs extremely rarely as well-formed crystals, most often forming microscopic, anhedral (irregular) grains or aggregates. It is usually colorless to white. Due to its microscopic size and rarity, its visual characteristics are difficult to assess with the naked eye, and identification requires advanced laboratory techniques. ## Physical Properties Crystals, when observed, have a tabular or equant habit. The mineral's hardness on the Mohs scale is approximately 5. It has a vitreous to resinous luster. It is a brittle mineral, with an uneven fracture. The calculated density is approximately 3.05 g/cm³. ## Colors and Varieties Silicocarnotite is typically colorless, white, or grayish. No colored or commercial varieties are known. ## History and Name The mineral was first described in 1883 by A. H. Cornwall in blast furnace slag from Pennsylvania, USA. The name refers to its chemical composition – the presence of silica – and its superficial and historical resemblance to carnotite. Its natural occurrence was confirmed much later, in 1964, in metamorphic rocks in Israel. For a long time, it was considered a synthetic product before being discovered in nature. ## Uses Silicocarnotite has no commercial or industrial applications. Its significance is purely scientific and mineralogical, particularly in the context of research into metamorphic processes and petrology.

Properties

Mohs hardness
5
Luster
Vitreous, Resinous
Streak
White
Density
3.05
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of silicocarnotite in field conditions or in a collection is impossible without specialized equipment. It requires analytical methods such as X-ray diffraction (XRD) or X-ray microanalysis (EDS/WDS) to confirm its chemical composition and crystal structure. It occurs as microscopic, colorless grains embedded in rock. ## Distinguishing from Similar Minerals It can be confused with many other colorless rock-forming minerals, such as quartz, apatite, or calcite, which often co-occur with it. Differentiation is only possible based on chemical and crystallographic analysis. ## Crystal Forms It forms microscopic, anhedral (irregular) or subhedral (poorly formed) grains. Rarely, small, tabular crystals up to several tens of micrometers in size are observed.

Geological environment

## Genesis Silicocarnotite is a product of high-temperature contact metamorphism. It forms in carbonate rocks (marbles) subjected to pyrometamorphism, often as a result of the combustion of underground coal or bitumen deposits, which heat the surrounding rocks to very high temperatures. It is also found in some limestone xenoliths within volcanic lavas and as a product of human activity in metallurgical slags. ## Mineral Associations It most commonly co-occurs with minerals typical of pyrometamorphic environments, such as larnite, spurrite, mayenite, brownmillerite, gehlenite, wollastonite, diopside, and calcite. ## Localities The most important natural occurrences are in the Hatrurim Formation in Israel and Palestine, where the mineral formed as a result of the combustion of bituminous rocks. It has also been reported in Jordan, in volcanic xenoliths in Germany (Eifel), Italy (Vesuvius), and Tajikistan. Synthetic silicocarnotite is known from metallurgical slags in many places around the world, including its original locality in Pennsylvania (USA).

Rarity

Very rare

For collectors

## Quality Criteria Silicocarnotite is not a mineral collected for traditional collecting purposes. Its value is purely scientific. Specimens of significance are those from well-documented localities that contain rich, though still microscopic, concentrations of the mineral, enabling scientific research. There is no market for ornamental specimens. ## Popular Localities From a scientific point of view, specimens from the classic localities in the Hatrurim Formation in Israel are most highly valued.

Care and storage

## Cleaning Due to its microscopic nature and occurrence as inclusions in the host rock, silicocarnotite specimens do not require and are not suitable for cleaning in the traditional sense of the word. ## What to Avoid Avoid contact with strong acids, which can damage the mineral. As a mineral embedded in rock, it is relatively stable, but the entire specimen should be protected from mechanical damage. ## Storage Specimens containing silicocarnotite should be stored in a dry place, away from chemicals. It is best to keep them in collector's boxes to protect them from dust and damage.

Sources

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