Possible Clues:

• Swirly marbles
• Ornamental stones
• A new stage setting may include them
• Kinds of quartz
• Which critic's are the gems?
• Stones that set up 27 across
• Stones might get the gas around 23 down
• A barrier that's composed of little stones
• They're seen at marble tournaments
• Perhaps a barrier is made of little stones like these