Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Hard (Adjective)

Hard as a brick.
—Anonymous

Hard as a cobble-stone.
—Anonymous

Hard as a cricket-ball.
—Anonymous

Hard as granite.
—Anonymous

Hard as hail stones.
—Anonymous

As hard as horn.
—Anonymous

Hard as marble.
—Anonymous

As hard as the rocks of Dundee.
—Anonymous

Hard as flint.
—Robert Burton

Hard as adamant.
—Robert Cawdray (A Treasurie or Store-house of Similies, 1600)

Hard as a 1907 prune.
—Helen Green

Hard as a barren stepmother’s slap.
—Lady Gregory

Hard as wire.
—John Heywood

As hard as the heart of a religious foe-curser.
—Oliver Wendell Holmes

Hard as an egg at Easter.
—Vincent Stuckey Lean (Collectanea)

Hard as nails.
—Vincent Stuckey Lean (Collectanea)

Hard as iron.
—Thomas Lodge

Hardeneth like the Adama[n]t.
—John Lyly

Fingers, hard as a lobster’s claws.
—Guy de Maupassant

Hard as the devil’s nagnails.
—G. F. Northall (Folk Phrases)

Hard as a sheet of brass.
—Ouida

Hard as a pine-knot.
—James K. Paulding

Hard as steel.
—William Shakespeare

Hard as the palm of ploughman.
—William Shakespeare

Hard as the push of death.
—Algernon Charles Swinburne

Hard as a piece of the nether millstone.
—Old Testament

Hard as Severn salmon dried in Wales.
—Ned Ward

Hard as a flint stone.
—Leonard Wright (A Display of Dutie)