Agrellite
Chemical formula: NaCa<sub>2</sub>Si<sub>4</sub>O<sub>10</sub>F
Agrellite is a rare sodium calcium silicate, forming characteristic bladed crystals with a pearly luster and intense pink fluorescence under UV light.
Properties
- Mohs hardness
- 5.5
- Luster
- Vitreous to pearly
- Streak
- White
- Density
- 2.88 - 2.90
- Cleavage
- Good on {110} and {1-10}
- Fracture
- Uneven to splintery
- Transparency
- Translucent to opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification The most important diagnostic feature of agrellite is its intense, pinkish-purple fluorescence under shortwave UV light. In daylight, it can be recognized by its white color, pearly luster on cleavage planes, and characteristic aggregate form – usually flattened, bladed crystal aggregates. ## Distinguishing from Similar Minerals Agrellite is sometimes confused with wollastonite, pectolite, or tremolite, which can also form white, fibrous aggregates. However, none of these minerals exhibit such characteristic and strong pink fluorescence under UV light. Wollastonite and tremolite occur in different parageneses (metamorphic rocks), and pectolite, though similar, is much more sensitive to acids. ## Crystal Forms Agrellite crystals are elongated and flattened, with a bladed or platy habit. They rarely occur as single, well-formed individuals. Most often, they form radial or randomly oriented aggregates, as well as compact and massive aggregates.
Geological environment
## Genesis Agrellite is a mineral typical of a very specific geological environment – peralkaline (agpaitic) nepheline syenites and associated pegmatites and gneisses. It forms in the late stages of crystallization of magma rich in sodium and fluorine, and poor in silica. ## Mineral Associations Minerals co-occurring with agrellite are often other rare alkaline minerals, which facilitates its identification. These include, among others, eudialyte (red), mosandrite, britholite, miserite, vlasovite, as well as various pyroxenes (e.g., aegirine) and amphiboles. Such a paragenesis is characteristic of Kipawa-type localities. ## Localities The most important and globally renowned locality for agrellite is the Kipawa alkaline complex in Témiscamingue, Quebec, Canada. The best collector specimens originate from there. Other confirmed localities include the Murun massif in Siberia (Russia) and the Dara-i-Pioz massif in Tajikistan.
Rarity
Rare
For collectors
## Quality Criteria The most highly valued agrellite specimens are those that form large, radial aggregates composed of well-formed, lustrous crystals. Pure, white color, strong luster, and intense fluorescence significantly increase the value of a specimen. Compositions where white agrellite contrasts with other colorful minerals, such as red eudialyte, are particularly sought after. ## Popular Localities By far, the most desired specimens by collectors come from the type locality in Kipawa, Quebec, Canada. They are considered the global standard for this mineral. Specimens from Russia are also available on the market, but rarely achieve the same quality as Canadian ones.
Care and storage
## Cleaning Agrellite specimens can be safely cleaned using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can damage delicate, fibrous crystal aggregates. ## What to Avoid This mineral is sensitive to strong acids. Although relatively stable, prolonged exposure to direct sunlight is recommended to be avoided, which is good practice for all fluorescent minerals. ## Storage Agrellite should be stored in a place protected from dust and mechanical damage. Due to its bladed or fibrous structure, specimens can be brittle, so it is advisable to place them in separate boxes or display cases, away from harder minerals.