Defernite

Chemical formula: Ca<sub>6</sub>(CO<sub>3</sub>)<sub>1.58</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>0.21</sub>(OH)<sub>7</sub>[Cl<sub>0.50</sub>(OH)<sub>0.08</sub>(H<sub>2</sub>O)<sub>0.42</sub>]

Defernite is a rare, colorless or white mineral from the silicate group, occurring as small, tabular crystals.

## Characteristics Defernite is a mineral with a complex chemical composition, belonging to the silicate group. It forms colorless to white, small crystals with a tabular or lamellar habit, which often arrange themselves into rosette-like or fan-shaped aggregates. Individual crystals are usually very small, rarely exceeding 1 mm in length, and are characterized by a vitreous luster. ## Physical Properties This mineral is relatively soft, with a hardness of 3 on the Mohs scale. It is transparent to translucent. Its density is slightly higher than that of quartz, at approximately 2.83 g/cm³. ## Colors and Varieties Defernite is typically colorless or white. No colored or commercial varieties have been identified. ## History and Name The mineral's name honors Jacques Defer (1919-1974), a French geologist and mine director in Bou Azzer, Morocco, where the mineral was first discovered. It was described and approved as a new mineral species in 1978 by Halil Sarp, Jean Bertrand, and Jacques Defer (posthumously). ## Uses Due to its rarity and small crystal size, defernite has no industrial application and is solely an object of interest for collectors specializing in rare minerals or minerals from specific localities.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
White
Density
2.83
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Defernite can be identified by its characteristic, small, tabular crystals, often forming fan-shaped or rosette-like aggregates. Its colorless or white color, vitreous luster, and low hardness (3 on the Mohs scale) are also important diagnostic features. It reacts with hydrochloric acid, which is a helpful identification characteristic. ## Distinguishing from Similar Minerals It can be confused with other white or colorless secondary minerals, such as calcite or some zeolites. It is distinguished from calcite by its crystal form (tabular, not rhombohedral) and its co-occurrence with minerals from the Bou Azzer deposit. Identification often requires advanced research methods, such as X-ray diffraction (XRD). ## Crystal Forms Defernite crystals are tabular, elongated, and flattened. They usually occur as radial, fan-shaped, or spherulitic aggregates, as well as rosettes.

Geological environment

## Genesis Defernite is a secondary mineral, formed in the oxidation zones of hydrothermal cobalt-arsenic deposits. It forms in calcite veins cutting through serpentinite rocks. ## Mineral Associations This mineral co-occurs with minerals such as calcite, talc, quartz, stichtite, lizardite, and also with minerals from the serpentine group. At its discovery site (Bou Azzer), it is also accompanied by cobalt and arsenic minerals. ## Localities The most important and classic occurrence of defernite is the Bou Azzer mining district, near Tazenakht, in the Ouarzazate Province of Morocco. This is its type locality. Beyond Morocco, its presence has also been reported in the Kombat Mine in Namibia.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals forming aesthetic, fan-shaped or rosette-like aggregates. Contrast with the rock matrix on which they occur is also important. Due to the small size of the crystals, specimens with larger (even up to 1 mm) and clearly visible aggregates are particularly sought after. ## Popular Localities By far the most known and valued defernite specimens come from its type locality - the Bou Azzer deposit in Morocco. Specimens from this location are the standard for this mineral.

Care and storage

## Cleaning Defernite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its low hardness, ultrasonic cleaners and mechanical cleaning should be avoided. If liquid is necessary, only distilled water is recommended. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Defernite is susceptible to scratches, so it should not be stored in contact with harder minerals. ## Storage It is recommended to store specimens in separate, padded collector boxes to protect them from mechanical damage and dust. It is best displayed in closed display cases.

Sources

Read more