Agrellite

Agrellite
Agrellite
	Agrellite showing fluorescence in ultraviolet light
General
Category	Inosilicates
Formula	NaCa2Si4O10F
IMA symbol	Are
Strunz classification	9.DH.75
Crystal system	Triclinic
Crystal class	Pinacoidal (1) ; (same H-M symbol)
Space group	P1
Identification
Color	White, grayish-white, greenish-white
Crystal habit	Lath - shaped like a small, thin plaster lath, rectangular in shape
Cleavage	perfect [110]
Mohs scale hardness	5.5
Luster	pearly
Streak	white
Diaphaneity	translucent
Specific gravity	2.88
Optical properties	biaxial
Refractive index	nα = 1.567 nβ = 1.579 nγ = 1.581
Birefringence	δ = 0.014
References

Agrellite (NaCa₂Si₄O₁₀F) is a rare triclinic inosilicate mineral with four-periodic single chains of silica tetrahedra.

It is a white to grey translucent mineral, with a pearly luster and white streak. It has a Mohs hardness of 5.5 and a specific gravity of 2.8. Its type locality is the Kipawa Alkaline Complex, Quebec, Canada, where it occurs as tabular laths in pegmatite lenses. Other localities include Murmansk Oblast, Russia, Dara-i-Pioz Glacier, Tajikistan, and Saima Complex, Liaoning, China. Common associates at the type locality include zircon, eudialyte, vlasovite, miserite, mosandrite-(Ce), and calcite.

Agrellite displays pink fluorescence strongly under shortwave and weakly under longwave ultraviolet light. The fluorescent activator is dominantly Mn²⁺, with minor Eu²⁺, Sm³⁺, and Dy³⁺.

It is named in honor of Stuart Olof Agrell (1913–1996), a British mineralogist at Cambridge University.