MERCURIAL

characterized by rapid and unpredictable change in mood

liable to sudden unpredictable change
SYN - erratic, fickle
"mercurial twists of tempermant"

"He couldn't handle her mercurial personality any longer and dumped the girl."

"It was a rather mercurial peace, which did little to ease the tension in the room."

"The boss was so mercurial that no-one knew what to expect."

"He had decided that he just needed to accept the mercurial nature of the earth and learn to live with such inconsistency."

"The christian herd follower wants consistency, calm and peace and dreads the often mercurial aspect of human nature."