Coyoteite
Chemical formula: NaFe<sup>3+</sup><sub>3</sub>S<sup>2-</sup><sub>5</sub>·2H<sub>2</sub>O
Coyoteite is a very rare, water-soluble iron and sodium sulfide, forming aggregates of fine, acicular crystals.
Properties
- Mohs hardness
- 1
- Luster
- Metallic
- Streak
- Black
- Density
- 2.21
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of coyoteite is its immediate solubility in water. In field conditions and collections, it can be recognized by its black color, metallic luster, and form of fine, acicular crystals forming coatings. It is an extremely soft and delicate mineral. ## Distinguishing from Similar Minerals It can be confused with other black, microcrystalline sulfides or oxides. However, none of the visually similar minerals (e.g., pyrolusite, some forms of marcasite) dissolve in water, which is a decisive test. ## Crystal Forms Coyoteite forms elongated, acicular or bladed crystals, often flattened. It occurs as radial aggregates, rosettes, and coatings and efflorescences on other minerals.
Geological environment
## Genesis Coyoteite is a secondary mineral. It forms as a result of weathering processes in an alkaline and reducing environment, in the presence of iron sulfides (such as pyrite or marcasite) and sodium-rich solutions. Its formation is associated with the oxidation of sulfides in sedimentary deposits. ## Mineral Associations This mineral coexists with other rare, water-soluble sulfates and sulfides. At the type locality, it was found in association with pyrite, quartz, calcite, gypsum, and other unidentified iron sulfates. ## Localities The only confirmed and described occurrence of coyoteite in the world is its type locality - Coyote Creek in San Juan County, southeastern Utah, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria For collectors, the size and richness of the aggregate on the rock matrix are most important. Since the crystals are microscopic, the primary assessment is of the surface area covered by the mineral and its undamaged condition. Specimens on a contrasting matrix are more desirable. Proper protection of the specimen from moisture is also crucial, indicating the care of previous owners. ## Popular Localities The only source of coyoteite specimens is its type locality in Coyote Creek, Utah, USA. All collectible material available on the market comes from this single location.
Care and storage
## Cleaning This mineral must absolutely not be wet cleaned, as it dissolves immediately in water. Mechanical cleaning is also inadvisable due to its extreme fragility. The safest way to remove dust is by using a stream of compressed air from a distance and with low force. ## What to Avoid Avoid contact with water, water vapor, and any moisture. Storage in a humid room leads to rapid destruction of the specimen. Also, avoid all chemicals, ultrasonics, and sudden temperature changes. ## Storage Coyoteite specimens must be stored in airtight, sealed containers, preferably with a desiccant (e.g., silica gel). They should be displayed away from light and heat sources, in stable conditions.