Combeite

Na_4.5Ca_3.5Si₆O_17.5(OH)_0.5IMA symbol: Cbegrandfathered

Combeite is a silicate mineral with the formula Na4.5Ca3.5Si6O17.5(OH)0.5, crystallizing in the trigonal system. It has a calculated density of 2.831 g/cm3. Its streak is white.

Photos

Combeite specimen photo — David Hospital · CC BY-SA 4.0 · Commons

Crystallography

Crystal system	trigonal crystal systemWikidata (CC0)
Space group	P 31 2 1
Cell (Å, °)	a = 10.464, b = 10.464, c = 13.176; α = 90, β = 90, γ = 120
Cell volume	1249.42 Å³, Z = 3
Axial ratios	1.0000:1:1.2592calculated from COD 9007720
Source structure	COD 9007720 (Acta Crystallographica, Section C, 1987) — 1 of 6 structures

Powder X-ray diffraction (calculated)

d (Å)	2.664	2.616	1.867	3.315	3.733	3.364
I/I₀	100	98.7	63.5	55.2	32.8	29.2

xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9007720; idealized occupancies, no preferred orientation.

Physical properties

Density (calculated)	2.831 g/cm³calculated from COD 9007720
Streak	whitesingle sourceWikidata (CC0)

Chemistry (calculated)

Molecular weight	700.73 g/molcalculated from the IMA formula
Composition (wt%)	Na 14.76%, Ca 20.02%, Si 24.05%, O 41.1%, H 0.07%

Classification

Nickel-Strunz (10th)	9.CJ.15aWikidata (CC0)
Nickel-Strunz (9th)	9.CJ.15Wikidata (CC0)