Amesite
Chemical formula: Mg<sub>2</sub>Al(AlSiO<sub>5</sub>)(OH)<sub>4</sub>
Amesite is a rare, greenish mineral from the serpentine group, valued for its well-formed, pseudohexagonal crystals.
Properties
- Mohs hardness
- 2.5-3
- Luster
- Vitreous, Pearly
- Streak
- White to greenish-white
- Density
- 2.77-2.83
- Cleavage
- Perfect on {001}
- Fracture
- Micaceous
- Transparency
- Translucent to transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Characteristic features of amesite include its pseudohexagonal, tabular crystals, often forming fan-shaped aggregates. The greenish color, pearly luster on cleavage planes, and relatively low hardness are also helpful in identification. The mineral is flexible but inelastic. ## Distinguishing from Similar Minerals It can be confused with other phyllosilicates of similar appearance, such as minerals from the chlorite group or micas (e.g., muscovite, phlogopite). It is distinguished from micas by the inelasticity of its lamellae. Distinguishing it from chlorites often requires advanced studies, such as X-ray diffraction (XRD), although amesite more frequently forms better-defined, hexagonal crystals. ## Crystal Forms Amesite crystallizes as small, hexagonal (pseudohexagonal) tablets and plates. These crystals often combine into rosette-like, fan-shaped, or radial aggregates. It also occurs in lamellar, scaly aggregates, and in massive forms.
Geological environment
## Genesis Amesite is a low-temperature hydrothermal mineral and a product of low-grade metamorphism. It forms in veins cutting aluminum-rich rocks, such as clay shales or emery deposits. It can also form in altered ultramafic igneous rocks. ## Mineral Associations This mineral often co-occurs with diaspore, corundum, magnetite, rutile, as well as minerals from the chlorite group and spinel. Depending on the locality, it may also be associated with vesuvianite, grossular, or clinozoisite. ## Localities The most important occurrences worldwide include the historical type locality in Chester, Massachusetts, USA. Beautiful, well-formed crystals come from the Saranovskiy mine in the Urals, Russia. Other known occurrences include the Keweenaw Peninsula in Michigan (USA), the Lake Baikal region in Russia, as well as some localities in Norway and South Africa (Postmasburg mine).
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with sharp, well-formed crystals with a distinct, pseudohexagonal outline. Aesthetically pleasing fan-shaped and rosette aggregates are also highly valued. The intensity and attractiveness of the green color, as well as the transparency of the crystals, significantly increase the specimen's value. Contrast with the rock matrix and the absence of mechanical damage are also important. ## Popular Localities Specimens from the Saranovskiy mine in the Urals, Russia, are considered among the best in the world, providing sharp, green crystals, often in attractive groups. Classic, though less readily available, are also specimens from the type locality in Chester, Massachusetts, USA.
Care and storage
## Cleaning Amesite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid The mineral is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. As a relatively soft mineral, it is susceptible to scratching. It should not be exposed to high temperatures. ## Storage Amesite specimens, especially those with well-formed crystals, should be stored in separate boxes or display cases to prevent abrasion and scratching by harder minerals. They should be protected from dust and moisture.