Marialite
General
Category	Tectosilicate
Formula (repeating unit)	Na4Al3Si9O24Cl
IMA symbol	Mar[1]
Strunz classification	9.FB.15
Crystal system	Tetragonal
Crystal class	Dipyramidal (4/m) (same H-M symbol)
Space group	I4/m
Unit cell	a = 12.06 Å, c = 7.572(3) Å; Z = 2
Identification
Color	Colorless, white, grey; pink, violet, blue, yellow, brown, orange-brown, pale green or reddish
Crystal habit	Typically flat, pyramidal striated crystals; massive, granular
Cleavage	Distinct on {100} and {110}
Fracture	Uneven to conchoidal
Tenacity	Brittle
Mohs scale hardness	5+1⁄2–6
Luster	Vitreous, pearly, resinous
Streak	White
Diaphaneity	Transparent to opaque
Specific gravity	2.55–2.74
Density	2.5–2.62 g/cm3
Optical properties	Uniaxial (−)
Refractive index	nω = 1.539–1.550 nε = 1.532–1.541
Birefringence	δ = 0.007 – 0.009
References	[2][3][4][5][6]

Marialite is a silicate mineral with a chemical formula of Na₄Al₃Si₉O₂₄Cl^[5][6] if a pure endmember or Na₄(AlSi₃O₈)₃(Cl₂,CO₃,SO₄) with increasing meionite content.^[3] Marialite is a member of the scapolite group and a solid solution exists between marialite and meionite, the calcium endmember.^[3] It is a rare mineral usually used as a collector's stone.

Marialite has tetragonal crystallography and a 4/m crystal class. It has a 4 fold rotation with 90° mirror planes. Crystals are usually prismatic with prominent forms of prisms and dipyramids.^[7]

Marialite belongs to a uniaxial negative optical class which means it has one circular section and a principal section shaped like an oblate sphenoid.

Marialite was first described in 1866 for an occurrence in the Phlegrean Volcanic complex, Campania, Italy. It was named by German mineralogist Gerhard vom Rath for his wife, Maria Rosa vom Rath.^[4][5]

Marialite occurs in regional and contact metamorphism: marble, calcareous gneiss, granulite and greenschist. It also occurs in skarn, pegmatite and hydrothermally altered volcanic rocks.^[4][5] This means that Marialite is formed in high pressure and/or high temperature environments.