noun
hyalite; water opal; Müller's glass
A mineralogical term for a colorless, glassy variety of opal. Used in geology and gemology contexts.
玉滴石は、火山岩の空洞に産することがある。
Hyalite can occur in cavities of volcanic rocks.
The exact derivation is uncertain; the kanji 玉 (jewel), 滴 (drop), and 石 (stone) suggest a 'jewel-drop stone', likely referring to its glassy, droplet-like appearance.