Darrellhenryite
Chemical formula: NaLiAl₂Al₆(BO₃)₃Si₆O₁₈(OH)₃O
Darrellhenryite is a very rare, black mineral from the tourmaline group, distinguished by its unique chemical composition with lithium and sodium.
Properties
- Mohs hardness
- 7
- Color
- intense to pale pink
- Luster
- Vitreous
- Streak
- pinkish white
- Density
- 3.03
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Transparent
- Crystal system
- Trigonal
Diagnostic features
## Identification Identification of darrellhenryite based on visual characteristics is practically impossible. It looks identical to other black tourmalines, especially schorl. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to determine its unique chemical composition, rich in sodium and lithium, with a simultaneous deficiency in the X position. ## Distinguishing from Similar Minerals It is most often confused with schorl, dravite, elbaite (opaque varieties like verdelite, indigolite), and other black tourmalines. Differentiation relies solely on chemical analysis – darrellhenryite is distinguished by a specific combination of Na, Li, and Al in its structure, which sets it apart from other members of the tourmaline supergroup. ## Crystal Forms Crystals are usually prismatic, columnar, with a characteristic rounded cross-section resembling a triangle (trigonal), typical of tourmalines. The faces of the columns often exhibit distinct, longitudinal striations.
Geological environment
## Genesis Darrellhenryite forms in complex lithium-rich granitic pegmatites. It is a mineral of the late stages of crystallization, forming in an environment abundant in boron, lithium, sodium, and aluminum. ## Mineral Associations This mineral co-occurs with other minerals typical of lithium pegmatites. In its type locality (Mogok, Myanmar), it was found in association with quartz, feldspars (albite), schorl, elbaite, and rossmanite. ## Localities Confirmed occurrences of darrellhenryite are extremely rare. It has been identified in the following localities: - Mogok, Pyin-Oo-Lwin District, Mandalay Region, Myanmar (Burma) - type locality. - Zlatá Idka District, Košice-okolie, Košice Region, Slovakia. - Menalo Mountains, Arcadia, Peloponnese, Greece.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a darrellhenryite specimen is primarily assessed based on the confirmation of its analytical identity. The most valuable specimens are well-formed, terminated crystals with distinct luster and striations, even if small. Association with other minerals, such as being embedded in a quartz matrix, is also important. ## Popular Localities The only source of collector-grade specimens so far is the Mogok region in Myanmar (Burma), from which the best-formed crystals originate.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. If necessary, compressed air can be used. Due to its rarity and scientific value, all invasive methods should be avoided. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage the mineral's surface. It should not be subjected to ultrasonic cleaning or sudden temperature changes. Despite its hardness, it is brittle and sensitive to impact. ## Storage Darrellhenryite specimens should be stored in separate, padded display boxes to prevent abrasions and mechanical damage. They should be protected from dust and moisture. As a stable mineral, it does not require special light conditions.