MgAl2O4
aluminum and magnesium oxide
Main color :
red
Other colors :
blue, colourless, yellow, black, orange, pink, green, purple
all the intensities of colors, from almost colorless to very dark
Color of streak :
white
Luster :
vitreous
Hardness :
8.0
Density :
3.54 to 4.62
Cleavage :
indistinct
Fracture :
conchoidal, uneven
Transparency :
transparent
some varieties are translucent and opaques
Refractive Index :
1.712 - 1.760
Double refraction :
0.000
Zero isotropic. The refractive index of red spinels is around 1.72
visible double refraction :
no
Dispersion :
0.020 (0.011)
Pleochroism :
absent
Number of colors :
1
Absorption spectrum : 685 - 675 - 665 - 595 - 490
For red spinel (chromium spectrum) 632,480,459 for gahnite. 632,585,555,478,458 for the blue (Iron spectrum )
blue spinel spectrum system
violet spinel spectrum system
red spinel spectrum system
Fluorescence :
variable
Strong for the red and pink colors, very low for blue
Inclusions :
aligned crystals of dolomite and apatite
Octahedra, tetrahedra and even more rarely dodecahedrons, often in twinned crystals and flattened.
Crystal system :
cubic
Astrological sign :
Aries, Taurus, Gemini, Cancer, Leo, Scorpio, Sagittarius, Capricorn, Aquarius