Paulkerrite
Chemical formula: [(H₂O)K]Mg₂(Fe³⁺₂Ti⁴⁺)(PO₄)₄(OF)(H₂O)₁₀·4H₂O
Paulkerrite is a rare, hydrated phosphate of potassium, magnesium, iron, and titanium, forming transparent, tabular crystals with perfect cleavage.
Properties
- Mohs hardness
- 3
- Luster
- Vitreous
- Streak
- White
- Density
- 2.36
- Cleavage
- {100} perfect
- Fracture
- Sub-Conchoidal
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Paulkerrite can be identified by its characteristic form – small, colorless or pale yellow, tabular crystals. A key diagnostic feature is its perfect cleavage in one direction, visible under magnification. Its low hardness (3 on the Mohs scale) is also helpful in identification. ## Distinguishing from Similar Minerals It can be confused with other colorless secondary minerals found in similar parageneses, such as gypsum or other phosphates. It is distinguished by its specific crystal habit (thin tablets) and perfect cleavage. Definitive confirmation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms thin, tabular crystals with a rectangular or bladed outline, flattened parallel to the cleavage plane. It occurs as individual crystals or small, loose aggregates on the surface of the host rock.
Geological environment
## Genesis Paulkerrite is a secondary mineral that forms in the oxidation zones of ore deposits. At its type locality (7U7 Ranch in Arizona), it formed in vugs within a lithium pegmatite that was altered by hydrothermal processes. ## Mineral Associations This mineral coexists with other phosphates and secondary minerals. At the type locality, it was found in association with strengite, rockbridgeite, jahnsite-(CaMnMg), scholzite, bermanite, zircon, quartz, and albite. ## Localities The most important and best-documented occurrence of paulkerrite is its type locality: 7U7 Ranch in Yavapai County, Arizona, USA. This is the only known locality for this mineral worldwide.
Rarity
Very rare
For collectors
## Quality Criteria The most prized paulkerrite specimens are those with well-formed, sharp, and transparent crystals, set on a contrasting rock matrix. Due to their small size, the quality of the crystal itself is crucial – its luster, lack of damage, and aesthetic arrangement. Specimens with visible associations of other rare phosphates are particularly sought after. ## Popular Localities The only source of collector specimens is the type locality in Arizona, USA. Material from this location is extremely rare and highly sought after by collectors specializing in mineral systematics, rare species, and micromounts.
Care and storage
## Cleaning Paulkerrite specimens should be cleaned with utmost care, using only compressed air to remove dust. Due to its softness and perfect cleavage, contact with water, brushes, and other mechanical tools should be avoided. ## What to Avoid Contact with all chemicals, including acids and detergents, should be avoided. The mineral is susceptible to mechanical damage, such as scratches, impacts, or abrasion. It should be protected from high temperatures, which can lead to dehydration and structural damage. ## Storage It is recommended to store paulkerrite specimens in specialized "micromount" boxes, which protect them from dust, humidity, and mechanical damage. Display should be away from direct sunlight and heat sources.