Book 27, Question 22
What makes some crystals see-through and others milky?
A perfectly clear crystal lets light pass straight through.
Cloudy crystals often have tiny cracks, bubbles, or other minerals trapped inside that scatter the light. Quartz can be clear, like glass, or milky white if full of tiny bubbles. Slow, calm growth tends to make clearer crystals because there is time for atoms to settle neatly. Rock crystal is the name for very clear quartz.