Rocks used as Altars
Source: TTT
Judges 6:20, 21, 26
And the angel of God said to him, “Take the meat and the unleavened bread, lay them on this rock, and pour out the broth.” And Gideon did so. / Then the angel of the LORD extended the tip of the staff that was in his hand and touched the meat and the unleavened bread. And fire flared from the rock and consumed the meat and the unleavened bread. Then the angel of the LORD vanished from his sight. / Then build a proper altar to the LORD your God on the top of this stronghold. And with the wood of the Asherah pole you cut down, take the second bull and offer it as a burnt offering.”
Judges 13:19
Then Manoah took a young goat and a grain offering and offered them on a rock to the LORD. And as Manoah and his wife looked on, the LORD did a marvelous thing.