Silicates — sodalite group · Sourced PROFILE
Lazurite
Na₆Ca₂Al₆Si₆O₂₄[(SO₄),S,Cl,(OH)]₂
A deep-blue sodalite-group silicate and the mineral that gives lapis lazuli its colour; it is recorded near Ishkoshim in the Pamir.
AT A GLANCE
- Formula
- Na₆Ca₂Al₆Si₆O₂₄[(SO₄),S,Cl,(OH)]₂
- Crystal system
- Cubic
- Space group
- P4̄3n
- Mohs hardness
- 5–5.5
- Density
- 2.38–2.45 g/cm³
- Optical character
- Isotropic; may be anomalously anisotropic
CRYSTALLOGRAPHY
Crystal form & structure
Dodecahedra, more rarely cubes, up to 5 cm; also granular, disseminated or massive.
HAND-SAMPLE PROPERTIES
Physical properties
- Cleavage
- Imperfect on {110}
- Fracture
- Uneven
- Tenacity
- Brittle
- Streak
- Bright blue
- Luster
- Vitreous
- Transparency
- Translucent to opaque
- Observed colours
- Deep blue, azure, violet-blue or greenish blue
LIGHT & OPTICS
Optical properties
- Optical class
- Isotropic; may be anomalously anisotropic
- Refractive index
- n = 1.502–1.522
- Fluorescence & electrical behaviour
- No diagnostic fluorescence is reported in the cited profile.
GEOLOGICAL SETTING
Formation
A contact-metamorphic mineral formed in limestones.
MINERAL COMPANY
Common associations
Calcite, pyrite, diopside, humite, forsterite, haüyne and muscovite
FIELD NOTES
How to identify it
Intense blue colour, bright blue streak, hardness about 5–5.5 and a matrix of calcite, pyrite and diopside are typical; chemistry or diffraction is needed to separate it from other blue sodalite-group minerals.
NAME & HISTORY
Where the name comes from
Named for its colour resemblance to azurite, from the Persian lazhward, meaning blue.
SCIENTIFIC SOURCE
Handbook of Mineralogy — Lazurite
External reference; factual profile paraphrased and attributed. Copyright remains with the publisher.
PROVENANCE
Documented occurrences
Lyadzhuar-Dara area near Ishkoshim, South-West Pamir · The Handbook of Mineralogy lists lazurite from Lyadzhuar-Darinsk near Ishkashim in the Pamir Mountains of Tajikistan. This record gives district context only, not collecting coordinates.
Sourced · District precisionHandbook of Mineralogy — Lazurite