SPINEL

Spinel comes in a wide range of colours, including Red, Pink, Blue, Violet, Purple, Orange, and even Grey or Black.
Red Spinel often resembles ruby and is highly prized.
Colour is due to trace elements:
Chromium --> Red & Pink
Iron -->Blue, Violet, Grey
Cobalt -->  Bright Blue
Notable Varieties:
Red Spinel --> Most valuable; often mistaken for ruby.
Blue Spinel --> Due to iron or cobalt.
Cobalt Spinel --> Rare, bright, vivid blue.
Color Change Spinel --> Rare, changes from blue to purple.
Star Spinel --> Shows asterism due to rutile inclusions.