The Hebrew kadkod refers to a sparkling, fiery gemstone, translated variously as ruby, carbuncle, or crystal. It appears only twice in the Hebrew Bible (Isaiah 54:12; Ezekiel 27:16), both in contexts of radiant splendor. Its exact identification is uncertain, but it belongs to the vocabulary of divine beauty and eschatological glory.
In Isaiah 54:12, God promises to set the gates of restored Jerusalem with kadkod as part of the covenant of peace. This passage belongs to the 'afflicted and storm-tossed' section where God comforts Zion after judgment — pledging to adorn her with jewels beyond imagination. The gemstone language in both Isaiah and Ezekiel signals that God's ultimate purposes for His people involve not just survival but radiance — a glory that reflects His own character. Revelation 21 echoes this imagery in the New Jerusalem adorned with every precious stone.