cubic Oxides
Spinel (Octahedron)
Formula MgAl2O4
Crystal Structure
#! Species: Spinel
#! System: Cubic (m3m)
#! Habit: Octahedral with octahedral inclusions
cubic[m3m]:{111}[inclusion:octahedral]
cubic
m3m
{111}
Quick Facts
Hardness
8.0
Specific Gravity
3.58
Refractive Index
1.712
Optical Character
Isotropic
Physical Properties
- Crystal System
- cubic
- Hardness (Mohs)
- 8.0
- Specific Gravity
- 3.58
- Cleavage
- Imperfect octahedral (rarely seen)
- Fracture
- Conchoidal
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.712
- Optical Character
- Isotropic
- Dispersion
- 0.02
- Pleochroism
- None
- Fluorescence
- Weak to moderate red (LWUV) in Cr-bearing; strong red in some
Characteristics
Colours
RedBlue (cobalt)PinkOrange (flame spinel)PurpleVioletGreyBlackColorlessColour-change
Localities
Myanmar (Mogok)Sri LankaTanzania (Mahenge)Vietnam (Luc Yen)TajikistanMadagascar
Common Inclusions
Octahedral crystalsFingerprints (healed fractures)Swallowtail twinsZircon with halosSpinel crystals
Known Treatments
Heat treatment (rare)
Crystal Forms
octahedron
Diagnostic Features
Isotropic; octahedral habit; lacks dichroism unlike ruby; often confused with corundum historically
Synthetics & Simulants
Known synthetic and simulant versions of Spinel
Related Minerals
Other minerals in the cubic system
