Dellaite

Where it forms, where it's found

Geological setting: Contact metamorphic. Polythermally metamorphosed limestone.
Type locality: Kilchoan
Ardnamurchan
Fort William and Ardnamurchan
Highland
Scotland
UK
56.6982°, -6.1042°

8recorded occurrences

Source · OpenStreetMap

Optical

Optical type: Biaxial (-) · 2V measured = 70°
Refractive index: 1.655 – 1.664
Surface relief: High
Principal indices: n_α 1.655 · n_γ 1.664

Michel-Lévy diagramhighlighted lineδ = 0.0090

Attainable Michel-Lévy rangeΔ ∈ [0, t·δ_max]90 nm1st order

Δ = 0Δ_max

Section thickness10 μmStage rotation0°

Thin-section mosaic70 grains · random 3D orientations

PPL

pleochroism per grain

XPL

independent extinctions · rotate the stage

Interference simulatorsingle grain · PPL ↔ XPL

PPL

pleochroism only · colour blends on rotation

XPL

interference colour · extinct every 90°

Retardation90 nm

Order1st order

XPL colour

Crystallography

Crystal system: Triclinic
Cell parameters: a = 6.815(4) Å · b = 6.937(3) Å · c = 12.890(6) Å
Cell angles: α = 90.71(4) ° · β = 97.68(4) ° · γ = 98.20(4) °
Ratio a:b:c: 1 : 1.018 : 1.891
Unit cell volume: 597.4 Å³
Comment: Akagane mine

Crystal structure

Chemical composition

Constituent elements: Mass composition breakdown
Element Atoms At. mass g/mol Mass g/mol Mass share
20CaCalcium Calcium 6 40.078 240.468
44.97%
8OOxygen Oxygen 13 15.999 207.987
38.89%
14SiSilicon Silicon 3 28.085 84.255
15.76%
1HHydrogen Hydrogen 2 1.008 2.016
0.38%
Total 534.726 100.00%
Mass share = atoms × atomic mass ÷ molar mass × 100
From IMA formula

Mass composition breakdown
Element	Atoms	At. mass g/mol	Mass g/mol	Mass share
20CaCalcium	Calcium	6	40.078	240.468	44.97%
8OOxygen	Oxygen	13	15.999	207.987	38.89%
14SiSilicon	Silicon	3	28.085	84.255	15.76%
1HHydrogen	Hydrogen	2	1.008	2.016	0.38%
	Total	534.726	100.00%

Synonyms

Dellaiet
IMA1964-005

In other languages

German: Dellait · IMA 1964-005
Italian: Dellaite
Chinese: 羟硅钙石

Classification

Strunz

10th ed.

9.BG.45

9SilicatesClass
9.BSorosilicatesDivision
9.BGSorosilicates with mixed SiO₄ and Si₂O₇ groups; cations in octahedral [6] and greater coordinationGroup
9.BG.45DellaiteSpecies

Dana

8th ed.

58.02.15.

58Sorosilicates Insular, Mixed, Single, and Larger Tetrahedral GroupsClass
58.02Insular, Mixed, Single, and Larger Tetrahedral Groups with cations in [6] and higher coordination; single and double groups (n = 1, 2)Type
58.02.15— unnamed intermediate level —Group
58.02.15. DellaiteSpecies

CIM

—

14.5.10

14Silicates not Containing AluminumClass
14.5Silicates of CaGroup
14.5.10DellaiteSpecies

Literature, links & citation

Citations

1965Fleischer, Michael (1965) New Mineral Names. American Mineralogist, 50 (11-12) 2096-2111
1965Agrell, S. O. (1965) Polythermal metamorphism of limestones at Kilchoan, Ardnamurchan. Mineralogical Magazine and Journal of the Mineralogical Society, 34 (268). 1-15 doi:10.1180/minmag.1965.034.268.01DOI: 10.1180/minmag.1965.034.268.01
1970Ganiev, R.M., Ilyukhin, V.V., Belov, N.V. (1970) Crystal structure of cement phase Y = Ca6[Si2O7][SiO4](OH)2. Soviet Physics - Doklady: 15: 85-87.
1970Ganiev, R.M., Ilyukhin, V.V., Belov, N.V. (1970) Crystal structure of cement phase Y = Ca6[Si2O7][SiO4](OH)2. Doklady Akademii Nauk SSSR: 190: 831-834.
2006Garbev, K., Gasharova, B., Beuchle, G., Stemmermann, P. (2006) An unusual phase transition Ca₂[SiO₃(OH)](OH) – Ca₆[Si₂O₇][SiO₄](OH)₂ (dellaite) as revealed by single crystal IR and X-ray powder diffraction. Acta Crystallographica Section A Foundations of Crystallography, 62 (a1). s207 doi:10.1107/s0108767306095869DOI: 10.1107/s0108767306095869

Cite this entry

@misc{mineral2026,
  author    = {Mineral Index editorial board},
  title     = {Dellaite — Mineral Index},
  year      = {2026},
  url       = {https://mineralindex.org/minerals/dellaite-1253},
  note      = {Accessed 2026-05-11}
}