Friedelite

Chemical formula: Mn²⁺₈Si₆O₁₅(OH)₁₀

Friedelite is a rare manganese silicate, forming platy or spherical crystals with a characteristic reddish-brown color and resinous luster.

## Characteristics Friedelite is a hydrated manganese silicate from the pyroxmangite group, chemically related to minerals such as rhodonite and pyroxmangite. It forms characteristic, well-developed platy crystals, often aggregated into rosette-like or radial forms. It also occurs as spherical, fibrous, or massive aggregates. Its appearance is very typical, and the luster on fresh fracture surfaces is distinctly resinous to vitreous. ## Physical Properties This mineral is characterized by a hardness of 4.5-5 on the Mohs scale, making it relatively soft. Its density is approximately 3.17-3.26 g/cm³. It is brittle, and its crystals exhibit perfect cleavage in one direction. Transparency ranges from transparent in thin splinters to translucent in larger masses. ## Colors and Varieties The predominant color of friedelite is reddish, orange-red, and reddish-brown. Pink, brown, and even colorless specimens are also found. The color is usually evenly distributed, although some aggregates may show some zonation. There are no named color varieties or commercial varieties. ## History and Name The mineral's name comes from Charles Friedel (1832-1899), a French chemist and mineralogist from the Sorbonne in Paris, who was also the curator of the mineral collection at the École des Mines. The mineral was first described in 1876 by Émile Bertrand based on specimens found in the Adervielle mine in the Pyrenees, France. ## Uses Friedelite has no industrial applications. It is valued solely as a collector's mineral due to its rarity, attractive color, and well-formed crystal habits.

Properties

Mohs hardness: 4-5
Color: Tan, brown, red, "beef steak" red-brown, dark brown
Luster: Resinous to vitreous
Streak: White
Density: 3.04
Cleavage: {0001}
Fracture: Sub-Conchoidal
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of friedelite include its characteristic reddish-brown or orange-red color, resinous luster, and typical forms of occurrence – platy crystals, often in rosette-like or spherical aggregates. Perfect cleavage in one direction is also an important clue. ## Distinguishing from Similar Minerals Friedelite is sometimes confused with rhodonite and rhodochrosite. It differs from rhodonite by its lower hardness (rhodonite 5.5-6.5) and often more resinous luster. Rhodochrosite is much softer (hardness 3.5-4), reacts with acids, and rarely forms platy crystals, preferring rhombohedral forms or spherical aggregates. Eudialyte, although similar in color, occurs in a completely different geological environment (nepheline syenites) and has a higher hardness. ## Crystal Forms Friedelite crystals are typically platy, with a hexagonal or pseudohexagonal outline. They often form fan-shaped, radial, or rosette-like aggregates. It also occurs as spherulitic (spherical), fibrous, granular, and massive aggregates.

Geological environment

## Genesis Friedelite is a mineral formed by metamorphic or metasomatic processes in manganese deposits. It forms under relatively low temperature and pressure conditions, often in veins cutting through manganese ore deposits or in manganese skarns. ## Mineral Associations This mineral often co-occurs with other manganese minerals, such as rhodochrosite, hausmannite, tephroite, rhodonite, pyrochroite, as well as with calcite, baryte, and franklinite (in the Franklin deposit). ## Localities The most important and classic localities for friedelite are the Adervielle mine in the Louron Valley in the Pyrenees (France) – the type locality. Excellent specimens come from the Franklin deposit in New Jersey (USA), where it forms beautiful crystals with franklinite. Other known occurrences include Harstigen and Långban in Sweden, the Wessels mine in Kuruman (South Africa), and Broken Hill in Australia.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals of intense, orange-red color. Rosette-like aggregates of transparent crystals are highly valued, as are aesthetic compositions with associated minerals, especially with white calcite or black franklinite, which create an attractive contrast. The size of the crystals and the absence of mechanical damage significantly increase the value of the specimen. ## Popular Localities The most famous and sought-after collector's specimens come from the historic Franklin deposit in New Jersey, USA. It yielded specimens of exceptional quality and color. Classic, though rarer, are also specimens from the type locality in France (Adervielle) and from the Swedish mines in Långban and Harstigen. In recent years, interesting specimens from South Africa have also appeared on the market.

Care and storage

## Cleaning Friedelite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. It should be dried immediately and thoroughly. ## What to Avoid Friedelite is sensitive to acids, which can damage it. Contact with all household and laboratory chemicals should be avoided. The mineral is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or exposed to sudden temperature changes. ## Storage Specimens should be stored in separate, padded boxes or display cases, away from harder minerals that could scratch them. Due to its perfect cleavage, pressure and vibrations should be avoided. Exposure to direct sunlight is not recommended, although there is no evidence of fading.