Semi-precious stone (3)
(Other definitions for jet that I've seen before include "Black; spurt" , "Black variety of lignite, used for ornaments" , "Spurt; aircraft" , "Rush" , "Deep black" .)
(Other definitions for topaz that I've seen before include "Precious stone - American hummingbird" , "Silicate gemstone" , "Type of gemstone" , "White/colourless mineral used as a gemstone" , "Yellow or pale blue gem" .)