Star spinel
| Refractive Index : 1.718 (+0.017 – 0.008) |
| Optical Characteristic : SR |
| Specific Gravity : 3.60 (+0.10 – 0.03) |
| Formula : MgAI2O4 |
| Crystal System : Cubic |
| Variety/Species : spinel |
| Species/Group : Spinel Group |
| Birefringence : none |
| Dispersion : 0.020 |
| Hardness : 8 |
| Toughness : good |
| Ultrasonic : Usually safe |
| Steam : usually safe |
| UV Long : Inert to strong |
| UV Short : Inert to weak |
| Pleochroism : None |
| Strength : N/A |
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| Pleochroism Colors : None |
| Heat : May change color |
| Acids : No reaction |
| Light : stable |
| Polish Luster : vitreous to subadamantine |
| Fracture : conchoidal |
| Fracture Luster : Vitreous |
| Clarity Type : N/A |
| Tones : 2-8 |
| Saturations : 1-5 |
| Cause of Color : Blue – iron, cobalt(rare); Red/pink – chromium |
| Enhancements : none |
| Cleavage : None |
| Color Range : Dark brownish red, purple, gray, black, reddish, purplish, grayish, blackish |
| Transparency : Semitransparent to semitranslucent |
| Phenomena : Aventurescence (rare), color change |
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| Separations : Star spinel from-
Star Garnet : RI, spectrum, SG (possibly) Star Ruby : optic character, magnification, pleochroism, optic character |
| Identifying Characteristics and information Tiny octahedral crystals arranged singly or in “fingerprint” patterns. May have iron oxide staining. |
| Spectral Data Red: 5400. Blue: 4330, 4580, 4600, 4780, 5080, 5550, 5850, 6350, 6750, 6850. |
| Trade Names and Misnomers Star Spinel |
Tags: cubic, Spinel, star spinel
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