All that glitters is not gold is a well-known saying, meaning that not everything that looks precious is precious. The expression, in various forms, originated in or before the 12th century[1] and may date from Aesop.[2]
The popular form of the expression is a corruption of a line in William Shakespeare's play, The Merchant of Venice, which employs a 17th century synonym for "glitters", "glisters". The line comes from a secondary plot of the play, the puzzle of Portia's boxes (Act II - Scene VII - Prince of Morocco):
All that glisters is not gold;
Often have you heard that told:
Many a man his life hath sold
But my outside to behold:
Gilded tombs do worms enfold.
Had you been as wise as bold,
Young in limbs, in judgement old
Your answer had not been inscroll'd
Fare you well, your suit is cold.
Panning for gold often results in finding pyrite, nicknamed fool's gold, which reflects substantially more light than authentic gold does. Gold in its raw form appears dull and does not glitter.
"Not all that glitters is gold" is an alternate formulation.[3][4][5]
The inverse of this expression, "All that glitters is gold," is a lyric in the Led Zeppelin song, "Stairway to Heaven", the Smash Mouth song, "All Star", and the Death in Vegas song, "All That Glitters".