October birthstone
October takes opal — silica spheres that diffract light into shifting play-of-color — and tourmaline, the borosilicate that grows in nearly every hue. Both have been called "the stone that holds the rainbow," and both are loved by artists for the same reason: no two specimens are alike.
Welo Opal / Ethiopian Opal
NATMohs 5.5-6 / RI 1.370-1.470
Orange Tourmaline
NATMohs 7-7.5 / RI 1.620-1.655
Green Tourmaline
NATMohs 7-7.5 / RI 1.624-1.644
Crystal Opal
NATMohs 5.5-6 / RI 1.37-1.47
Synthetic Opal
SYNMohs 5-6 / RI 1.37-1.50
Dravite
NATMohs 7-7.5 / RI 1.610-1.650
Assembled Opal (Doublet/Triplet)
IMIMohs 5.5-6 / RI 1.37-1.50
Pink Tourmaline
NATMohs 7-7.5 / RI 1.620-1.640
Fire Opal
NATMohs 5.5-6 / RI 1.37-1.47
Black Opal
NATMohs 5.5-6 / RI 1.37-1.47
Black Tourmaline (Schorl)
NATMohs 7-7.5 / RI 1.625-1.655
Boulder Opal
NATMohs 5.5-6 / RI 1.37-1.47
White Opal
NATMohs 5.5-6 / RI 1.37-1.47
Matrix Opal
NATMohs 5.5-6.5 / RI 1.450
Mexican Opal
NATMohs 5.5-6 / RI 1.370-1.470
Rubellite
NATMohs 7-7.5 / RI 1.620-1.640