Srebrodolskite
Chemical formula: Ca₂Fe³⁺₂O₅
Srebrodolskite is a rare calcium iron oxide, forming microscopic, black grains in thermally altered limestone rocks.
Properties
- Mohs hardness
- 5.5
- Color
- Black
- Luster
- Metallic
- Streak
- Grayish brown
- Density
- 4.04
- Cleavage
- Cleavage on (h0l)
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of srebrodolskite is possible almost exclusively by laboratory methods, such as chemical analysis (EDS) and X-ray diffraction (XRD), due to its microscopic size. Under a reflected light ore microscope, it exhibits characteristic high reflectivity and weak pleochroism from gray to grayish-brown. ## Distinguishing from similar minerals It can be confused with other black, opaque ore minerals, such as magnetite, hematite, or ilmenite, which often co-occur in similar environments. Differentiation requires specialized instrumental analyses. Unlike magnetite, srebrodolskite is not magnetic. ## Crystal forms It most often occurs as irregular, anhedral grains disseminated in the rock. Less commonly, it forms very small, tabular or lath-like crystals, usually grouped into small aggregates.
Geological environment
## Genesis Srebrodolskite is a mineral of metamorphic origin. It forms under conditions of high-grade contact metamorphism, in contact zones of magmatic intrusions with carbonate rocks (limestones, marls). It forms as a result of chemical reactions at high temperatures, often within xenoliths (fragments of sedimentary rocks) in lavas. ## Mineral associations This mineral co-occurs with other minerals typical of skarns and the sanidinite facies, such as mayenite, larnite, brownmillerite, shulamitite, calcite, ettringite, afwillite, jennite, as well as magnetite and hematite. ## Localities The most important and classic localities of srebrodolskite are: - Srebrodol deposit, Eastern Rhodopes, Bulgaria (type locality). - Hatrurim Formation in Israel and the Palestinian Territories, where it occurs in rocks formed by natural combustion of bitumens. - Volcanoes in the Eifel mountains, Germany (e.g., Ettringer Bellerberg). - Vesuvius in Italy.
Rarity
Very rare
For collectors
## Quality criteria The quality of srebrodolskite specimens is assessed primarily from a scientific perspective. The most valuable samples are those in which the mineral is well-formed (though still microscopic) and occurs in a rich association with other rare minerals. Confirmation of identification by analysis (e.g., EDS) significantly increases the specimen's value. ## Popular localities The most known and valued specimens by micromineral collectors come from the Hatrurim complex (Israel) and from the volcanoes in the Eifel region of Germany. Specimens from these localities often contain rich parageneses of rare contact minerals.
Care and storage
## Cleaning Specimens containing srebrodolskite, due to the microscopic nature of the mineral and its occurrence within the host rock, generally do not require cleaning. If necessary, compressed air can be used to remove dust. Avoid washing with water, which could damage co-occurring minerals. ## What to avoid Avoid contact with acids and other chemicals that may react with both srebrodolskite and the host rock (most often calcite). The mineral is stable, but it should be protected from mechanical damage. ## Storage Specimens should be stored in stable conditions, away from dust and moisture. It is best to keep them in sealed collector boxes or display cases to prevent accidental abrasion of the delicate rock surface.