Flint is a variety of quartz that, due to its extreme hardness, is easily shaped by flaking. Known and used since very ancient times, flint was used by the Israelites for knives, ax heads, arrow heads, spear heads and starting fires. In more modern times, the classic flintlock rifle of the pioneer era used flint sparks to ignite the gunpowder charge, and flint is still widely used today for such things as lighting oxy-acetylene welding torches and in lighters used by campers and smokers.
Flint is mentioned in The Bible both literally, as used by people during Bible History, and figuratively, in terms of its hardness, as an analogy for either righteous determination or foolish stubbornness. Some examples of both:
"The Lord your God, Who brought you out of the land of Egypt, out of the house of bondage, Who led you through the great and terrible wilderness, with its fiery serpents and scorpions and thirsty ground where there was no water, Who brought you water out of the flinty rock" (Deuteronomy 8:14-15 RSV) (see Rock Of Ages and Wilderness Journey)
"Then Zipporah took a flint and cut off her son's foreskin, and touched Moses' feet with it, and said, "Surely you are a bridegroom of blood to me!" So He let him alone. Then it was that she said, "You are a bridegroom of blood," because of the circumcision." (Exodus 4:25-26 RSV)
"At that time The Lord said to Joshua, "Make flint knives and circumcise the people of Israel again the second time." So Joshua made flint knives, and circumcised the people of Israel at Gibeath-haaraloth. And this is the reason why Joshua circumcised them: all the males of the people who came out of Egypt, all the men of war, had died on the way in the wilderness after they had come out of Egypt. Though all the people who came out had been circumcised, yet all the people that were born on the way in the wilderness after they had come out of Egypt had not been circumcised." (Joshua 5:2-5 RSV)
"For the Lord God helps me; therefore I have not been confounded; therefore I have set my face like a flint, and I know that I shall not be put to shame; He who vindicates me is near." (Isaiah 50:7-8 RSV)
Fact Finder: Is a very hard mineral such as flint (NASB, NIV) or adamant (RSV, KJV) used as an analogy for the attitude of someone who refuses to repent?