be clear as crystal

Concise Bible Dictionary:

1. zekukith (Job 28:1717The gold and the crystal cannot equal it: and the exchange of it shall not be for jewels of fine gold. (Job 28:17)), probably glass highly ornamented, such as was made in Egypt: it is here classed with gold; but wisdom, the gift of God, far exceeds such things in value.

Strong’s Dictionary of Greek Words:

Greek:
κρυσταλλίζω
Transliteration:
krustallizo
Phonic:
kroos-tal-lid’-zo
Meaning:
from 2930; to make (i.e. intransitively, resemble) ice ("crystallize")
KJV Usage:
be clear as crystal