Lileyite

Chemical formula: Ba₂Ti⁴⁺₂Na(NaFe²⁺)Mg(Si₂O₇)₂O₂F₂

Lileyite is a very rare mineral from the sorosilicate group, a member of the lamprophyllite group, found in ultramafic igneous rocks.

## Characteristics Lileyite is an extremely rare mineral belonging to the sorosilicates of the lamprophyllite group. It forms very small, lath-like or platy crystals, usually less than 1 mm in size, which can occur as radial aggregates. It is brown to dark brown and exhibits strong pleochroism in shades of brown and yellow. ## Physical properties Lileyite crystals have a luster described as vitreous to resinous. The mineral is brittle. Due to the small size of the crystals, many of its physical properties, such as hardness or density, have not been precisely measured, but only calculated based on its chemical composition and unit cell parameters. ## Colors and varieties This mineral occurs in uniform colors from brown to dark brown. No varieties have been distinguished. ## History and name Lileyite was first described in 2002 by A.R. Chakhmouradian and R.H. Mitchell. Its name honors Peter E. Liley, a Canadian geologist who first identified the rock containing this mineral in the Red Wine magmatic complex in Labrador, Canada. It was approved by the International Mineralogical Association (IMA) under number IMA2001-034. ## Uses Lileyite has no industrial or commercial applications. Its significance is purely scientific and as a collector's item, as a unique member of the lamprophyllite group.

Properties

Mohs hardness
3-4
Color
Brown
Luster
Vitreous to Resinous
Streak
White
Density
3.776
Cleavage
on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of lileyite is impossible without advanced analytical techniques. This requires chemical analysis (e.g., by electron microprobe) and X-ray diffraction (XRD) methods to confirm the crystal structure. Visual characteristics under the microscope include its lath-like habit and strong pleochroism. ## Distinguishing from similar minerals Lileyite is visually very similar to other minerals of the lamprophyllite group, such as lamprophyllite, ericssonite, or barytolamprophyllite. Distinguishing them relies solely on detailed chemical analysis, especially the content of barium, sodium, iron, and magnesium. ## Crystal forms Lileyite forms flattened, lath-like or platy crystals, elongated along the b-axis. These crystals often occur as radial or stellate aggregates, intergrown with other minerals of the host rock.

Geological environment

## Genesis Lileyite forms under specific magmatic conditions, within agpaitic (alkali-rich, alumina-poor) ultramafic rocks. In the type locality (Red Wine, Canada), it occurs in pegmatite veins cutting nepheline syenites. ## Mineral associations This mineral coexists with other rare alkaline minerals. Its paragenesis includes eudialyte, lamprophyllite, nepheline, arfvedsonite, barytolamprophyllite, and magnesium fluoride (sellaite). ## Localities The only confirmed and thoroughly described occurrence of lileyite in the world is its type locality: the Red Wine intrusive complex in central Labrador, Newfoundland and Labrador province, Canada.

Rarity

Extremely rare

For collectors

## Quality criteria As a mineral primarily of micromount significance, the main quality criterion for a lileyite specimen is the richness and distinctness of the crystals in the field of view. The most desirable specimens are those showing well-formed, radial aggregates of lileyite, clearly contrasting with the host rock. The presence of other rare associated minerals, such as eudialyte, also increases the scientific and collector's value of the specimen. ## Popular localities The only source of lileyite specimens is its type locality in Canada (Red Wine complex). Material from this location is extremely difficult to acquire and appears on the collector's market sporadically, mainly in circulation among specialized collectors of rare minerals.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, lileyite specimens embedded in rock matrix should not be cleaned mechanically or chemically. Any contaminants, such as dust, should only be removed with compressed air or a very soft brush. ## What to avoid Avoid contact with any chemicals, including acids and bases. Specimens should not be subjected to ultrasonic cleaning. Protect them from shocks and impacts due to the mineral's brittleness. ## Storage Lileyite specimens should be stored in stable conditions, away from dust and direct sunlight. The safest way is to keep them in sealed perky boxes, which protects them from mechanical damage and contamination.

External references

Sources

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