Aqualite

Aqualite is a very rare mineral of the eudialyte group, with formula (H₃O)₈(Na,K,Sr)₅Ca₆Zr₃SiSi(Si₂₄O₆₆)(OH)₉Cl.^[2][3] The formula given does not show the presence of cyclic silicate groups. The original formula was extended to show the presence of silicon at both M3 and M4 sites, according to the nomenclature of the eudialyte group.^[4] Aqualite is unique among the eudialyte group in being hydronium-rich (the only other eudialyte-group species with essential hydronium, is the recently discovered ilyukhinite).^[2] Among the other representatives of the group it also distinguish in splitting of the M1 site into two sub-sites, both occupied by calcium. Thus, its symmetry is lowered from typical for most eudialytes R3m (or R-3m) to R3. The name refers to high content of water in the mineral.^[3][4]

Aqualite
General
Category	Silicate mineral, cyclosilicate
Formula	(H3O)8(Na,K,Sr)5Ca6Zr3Si26O66)(OH)9Cl
IMA symbol	Aq[1]
Strunz classification	9.CO.10
Crystal system	Trigonal
Crystal class	Pyramidal (3) H-M symbol: (3)
Space group	R3
Unit cell	a = 14.08, c = 31.24 [Å] (approximated); Z = 3
Identification
Color	Pink (pale)
Crystal habit	idiomorphic crystals (max. 3 cm)
Cleavage	None
Fracture	Conchoidal
Mohs scale hardness	4–5
Luster	Vitreous
Streak	White
Diaphaneity	Translucent
Density	2.58 (measured), 2.66 (calculated)
Optical properties	Uniaxial (+)
Refractive index	nω = 1.57, nε = 1.57 (approximated)
Pleochroism	Colorless to pink (W), pink (E)
Ultraviolet fluorescence	dull yellow (weak)
References	[2][3]

Notes on chemistry

Elements occurring as admixtures in aqualite include barium, iron, rare-earth elements (including cerium), titanium, aluminium and trace niobium.^[3]

Occurrence and association

Aqualite was discovered among peralkaline pegmatites of the Inagli massif, Sakha-Yakutia, Russia. Associated minerals are aegirine, batisite, eckermanite, innelite, lorezenite, natrolite, microcline, thorite, and galena.^[3]

Origin

Aqualite is thought to be formed by ion exchange transformation of a precursor mineral.^[3]