When Maxwells miner minions mine moon glass chunks on the Lunar Island or Vitre Oases in the Lunar Grotto it plays the same sound as mining a rock boulder. When you mine it manually yourself it plays the correct "glassy" sound.
1. Summon Maxwells Miner minions.
2. Have them mine Moon Glass on the Lunar Island
3. Have them mine Vitre Oases in the Lunar Grotto