Chromatite
Chemical formula: CaCr<sup>6+</sup>O<sub>4</sub>
Chromatite is an extremely rare, naturally occurring calcium chromate, forming microscopic, bright yellow crystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous
- Streak
- Pale yellow
- Density
- 3.4
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification Chromatite is recognized by its characteristic bright yellow color, the form of small, tabular crystals, and its specific occurrence environment. Due to its size, its identification requires the use of a microscope or a high-magnification loupe. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction. ## Distinguishing from Similar Minerals Due to the unique geological environment in which it occurs, it is rarely confused with other minerals. Under other conditions, it could theoretically be mistaken for other secondary, yellow chromate or uranium minerals, but its mineral associations are a key diagnostic clue. ## Crystal Forms Chromatite crystals are very small, typically tabular or short-prismatic. They crystallize in the tetragonal system, forming simple, quadratic shapes. They occur as single, scattered crystals or small aggregates on the surface of the host rock.
Geological environment
## Genesis Chromatite forms under unique conditions of pyrometamorphism, i.e., thermal alteration of sedimentary rocks at high temperatures and low pressures. Its formation is associated with the combustion processes of natural bitumens contained in marls, leading to the formation of high-temperature mineral phases. It is a mineral typical of the Hatrurim Formation (the "Mottled Zone") in the Middle East. ## Mineral Associations This mineral co-occurs with other rare minerals formed in pyrometamorphic processes, such as calcite, spurrite, larnite, brownmillerite, and also with other chromates, e.g., bentorite. ## Localities The most important and best-documented occurrences of chromatite in the world are located in Israel and the Palestinian territories, within the Hatrurim Formation. It has also been reported in Jordan. These are the only confirmed locations of its occurrence.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a chromatite specimen is primarily assessed based on the size and development of the crystals, which is a rarity. Specimens with visible, sharp, undamaged crystals of intense yellow color under a microscope are most valued. The contrast with associated minerals (matrix) is also important. ## Popular Localities The only source of collector specimens is the Hatrurim Formation in Israel and Palestine. Specimens from this locality are the standard for this mineral.
Care and storage
## Cleaning Chromatite specimens should generally not be cleaned mechanically or chemically due to their extreme delicacy and microscopic crystal size. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Contact with water should be avoided. ## What to Avoid Contact with acids and other chemicals must be strictly avoided. The crystals are very brittle and sensitive to mechanical damage, so vibrations, impacts, and friction should be avoided. It should not be subjected to cleaning in ultrasonic cleaners. ## Storage Chromatite specimens should be stored under stable conditions, in sealed "micromount" boxes that protect them from dust, moisture, and physical damage. Exposure to direct sunlight should be avoided, although there is no evidence of fading.