January birthstone (6)
I believe the answer is:
garnet
'january birthstone' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for garnet that I've seen before include "Precious stone, usually red" , "Deep red precious stone" , "Glassy red, yellow or green gemstone" , "Semi-precious stone of deep transparent red" , "Semi-precious stone of argent type" .)