Balliranoite

(repeating unit)(Na,K)₆Ca₂(Si₆Al₆O₂₄)Cl₂(CO₃)IMA symbolBlr^[1]Crystal systemHexagonalCrystal class6 - PyramidalSpace groupP6₃Unit cella = 12.696 Å, c = 5.327 Å, V = 743.6 Å³, Z = 1IdentificationColorColorlessCrystal habitPrismaticCleavagePerfect on (10-10)FractureIrregular/UnevenTenacityBrittleMohs scale hardness5LusterVitreousStreakWhiteDensity2.48 g/cm³Optical propertiesuniaxial positiveReferences^{[2] [3][4]}

Balliranoite ((Na,K)₆Ca₂(Si₆Al₆O₂₄)Cl₂(CO)₃) is a mineral that was discovered at Monte Somma – Vesuvio volcanic complex, Campania, Italy. This mineral is named in honor of Paolo Ballirano (b. 1964), Italian crystallographer and professor in the Department of Earth Sciences, University of Rome ‘‘La Sapienza’’, who has made important contributions to the crystal chemistry of cancrinite-group minerals.

Balliranoite is found in an alkaline skarnlike rock composed of orthoclase, phlogopite, clinohumite, calcite, diopside, pargasite, haüyne, apatite and balliranoite,^[5] as product of the metasomatic interactions between alkaline magma and limestone. These chemical alterations by hydrothermal and other fluids replace elements in the chemical structure, changing the mineral composition of the rock.

The idealized formula for balliranoite is (Na,K)₆Ca₂(Si₆Al₆O₂₄)Cl₂(CO₃), and the empirical formula based on 12 Si atoms with isomorphic substitution by Al atoms is: Na_4.70Ca_2.53K_0.73(Si_6.02Al_5.98O_23.995)Cl_2.34(C_O3)_0.82(SO4_0.27*0.12H₂O.^[3] This is a uniaxial (+) mineral with w = 1.523(2), e = 1.525(2), composed of the following compounds:^[3]

Compound	wt%	Range
Na2O	13.05	12.80-13.24
K2O	3.08	3.01-3.16
CaO	12.70	12.56-12.85
Al2O3	27.28	27.17-27.42
SiO2	32.38	32.23-32.55
CO2	3.24	3.18-3.30
SO3	1.96	1.79-2.10
Cl	7.43	7.20-7.70
H2O	0.19	0.15-0.23
-O=Cl2	-1.68	-
Total	99.63	-

The powder diffraction data for balliranoite is:

d-spacing (Å)	Intensity
4.797	(100)
3.669	(57)
3.281	(73)
2.754	(16)
2.662	(58)
2.648	(13)
2.446	(31)
2.120	(18)

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