Jeffreyite
Chemical formula: (Ca,Na)₂(Be,Al)Si₂(O,OH)₇
Jeffreyite is a very rare mineral from the melilite group, forming small, colorless to pale yellow crystals with a vitreous luster.
Properties
- Mohs hardness
- 5
- Color
- Colourless
- Luster
- Vitreous
- Streak
- white
- Density
- 2.99
- Cleavage
- {001}, {110}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Jeffreyite identification is primarily based on its specific occurrence environment (rodingitic rocks within serpentinites) and associated minerals, such as vesuvianite, diopside, or grossular. Characteristic features include small, tabular crystals with a vitreous luster. However, definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Distinguishing from similar minerals It can be confused with other colorless or pale yellow minerals found in the same environment, e.g., some forms of grossular or vesuvianite. It is distinguished from them by its lower hardness and characteristic tabular crystal habit. ## Crystal forms Jeffreyite crystallizes in the tetragonal system, forming thin, tabular crystals with a square or octagonal outline. It also occurs as short prismatic crystals.
Geological environment
## Genesis Jeffreyite is a mineral of metamorphic origin. It forms under specific conditions within rodingites – metasomatic rocks rich in calcium and silicon, which develop as a result of the serpentinization processes of ultramafic rocks (peridotites). ## Mineral associations It most commonly co-occurs with minerals such as vesuvianite, diopside, grossular, zircon, titanite, and members of the serpentine group. ## Localities The only confirmed and thoroughly described locality of jeffreyite in the world is its type locality – the inactive Jeffrey quarry in Asbestos (now Val-des-Sources), in the Estrie region, Quebec province, Canada.
Rarity
Very rare
For collectors
## Quality criteria The quality of a jeffreyite specimen is primarily determined by the size and formation of its crystals. The most prized specimens are those with clearly visible, well-formed, tabular crystals, even if they are less than a millimeter in size. The aesthetic composition with associated minerals, especially contrasting vesuvianite or grossular, is also important. The clarity and transparency of the crystals increase the specimen's value. ## Popular localities The only source of collector specimens is the Jeffrey mine in Quebec, Canada. Since the mine has been inactive for years, new specimens do not enter the market, and those available come from old collections, making them even rarer.
Care and storage
## Cleaning Jeffreyite specimens should be cleaned very carefully, using only a soft brush to remove dust. Due to its brittleness and small crystal size, ultrasonic cleaners and mechanical cleaning should be avoided. The use of water is not recommended. ## What to avoid Contact with all chemicals, including acids and bases, should be avoided. The mineral is brittle, so it must be protected from impacts and sudden temperature changes. ## Storage Jeffreyite specimens, due to their small size and rarity, are best stored in specialized display boxes or small, padded containers that protect them from mechanical damage and dust.