Vránaite
Chemical formula: Al₁₆B₄Si₄O₃₈
Vránaite is an extremely rare aluminum and boron silicate, forming colorless to white, tabular crystals in pegmatites.
Properties
- Mohs hardness
- 4.5
- Color
- Colorless
- Luster
- Vitreous
- Streak
- White
- Density
- 2.99
- Cleavage
- None
- Fracture
- Irregular/Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of vránaite is almost exclusively possible using advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). Visually, it is practically impossible to distinguish from many other colorless pegmatitic minerals without specialized equipment. ## Distinguishing from similar minerals It can be confused with small crystals of quartz, albite, beryl (goshenite), or danburite, which occur in similar environments. Differentiation requires analysis of chemical composition (presence of boron and aluminum in specific proportions) and crystal structure. ## Crystal forms It forms flattened, tabular or bladed crystals with a rectangular cross-section. Crystals are usually very small, up to 1 mm long and up to 0.1 mm thick. They occur as single, isolated crystals embedded in quartz or albite.
Geological environment
## Genesis Vránaite forms in the late stage of crystallization of complex granitic pegmatites, rich in lithium, boron, and phosphorus. It is a hydrothermal or pneumatolytic mineral, crystallizing in voids and fractures of the host rock. ## Mineral associations This mineral coexists with quartz, albite (cleavelandite variety), schorl, elbaite, lepidolite, microcline, cassiterite, danburite, and apatite. ## Localities The only confirmed locality of vránaite in the world is its type locality: the pegmatite quarry in Vlastějovice near Ledeč nad Sázavou in the Vysočina Region, Czech Republic.
Rarity
Extremely rare
For collectors
## Quality criteria The quality of a vránaite specimen is primarily determined by the possibility of unambiguous identification of the crystals. The most valuable specimens are those with well-formed, even microscopic, crystals that are clearly visible against the matrix rock (most often quartz). Crystal size is a key factor – any specimen with crystals exceeding 0.5 mm is considered exceptional. ## Popular localities The only source of specimens is the type locality in the Czech Republic. Material from this location is extremely limited and rarely appears on the collector's market.
Care and storage
## Cleaning Due to the extreme rarity and small size of the crystals, vránaite specimens usually do not require cleaning. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemical agents. ## What to avoid Avoid all mechanical cleaning methods (brushes, ultrasonics) and contact with chemicals, acids, and bases. The crystals are fragile and embedded in the matrix rock, so they should be protected from impacts and vibrations. ## Storage Specimens should be stored in stable conditions, in a closed "micromount" box, to protect them from dust, mechanical damage, and sudden temperature changes. It is not sensitive to light.