Lorenzenite

Lorenzenite is a rare sodium titanium silicate mineral with the formula Na₂Ti₂Si₂O₉ It is an orthorhombic mineral, variously found as colorless, grey, pinkish, or brown crystals.

Lorenzenite
Doubly terminated crystal of Lorenzenite, 2.5 cm tip to tip, from Lovozero Massif, Kola Peninsula, Russia
General
Category	Silicate mineral
Formula (repeating unit)	Na2Ti2[O3|Si2O6]
Strunz classification	9.DB.10
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H–M Symbol: (2/m 2/m 2/m)
Space group	Pbcn
Unit cell	a = 8.71, b = 5.23 c = 14.48 [Å]; Z = 4
Identification
Color	Pale purple-brown, pale pink to mauve, brown to black
Crystal habit	Equant, bladed, prismatic, to needlelike crystals; fibrous, felted, lamellar aggregates
Cleavage	Distinct/good on {010}
Fracture	Irregular/uneven
Mohs scale hardness	6
Luster	Adamantine, vitreous, sub-metallic, dull
Streak	White to pale brown
Diaphaneity	Transparent, opaque
Specific gravity	3.42 - 3.45
Optical properties	Biaxial (-)
Refractive index	nα = 1.910 - 1.950 nβ = 2.010 - 2.040 nγ = 2.030 - 2.060
Birefringence	δ = 0.120
Pleochroism	Weak
2V angle	Measured: 38° to 41°
Ultraviolet fluorescence	Pale yellow to dull green under SW UV
References	[1][2][3]

It was first identified in 1897 in rock samples from Narsarsuk, Greenland.[2] In 1947 it was discovered to be the same as the mineral ramsayite (now a synonym of lorenzenite), discovered in the 1920s in the Kola peninsula of Russia. It is also found in northern Canada.

It occurs in nepheline syenites and pegmatites in association with aegirine, nepheline, microcline, arfvedsonite, elpidite, loparite, eudialyte, astrophyllite, mangan-neptunite, lavenite, rinkite, apatite, titanite and ilmenite.[1]

It was named in honor of Danish mineralogist Johannes Theodor Lorenzen (1855–1884).[2]

References

1. Handbook of Mineralogy
2. Mindat
3. Webmineral