“Diamonds are only lumps of coal that stuck to their jobs” is the first line of a much-reprinted 1922 poem by Minnie Richards Smith. “He was a pessimist that said a diamond is only a chunk of coal, and an optimist who added, ‘But it made good under pressure’” was cited in 1952.
 
“A diamond is a chunk of coal that made good under pressure” was cited in print in 1962 and is the version that is now used the most. The “made good under pressure” saying has been used in business and in sports.
 
 
Chronicling America
17 November 1922, Glasgow (MT) Courier, pg. 6, col. 4:
STICK TO YOUR JOB
Diamonds are only chunks of coal
That stuck to their jobs, you see
If they’d petered out like most of us do
Where would the diamonds be?
 
It isn’t the fact of making a start
It’s the sticking that counts, I’ll say.
It’s the fellow that knows not the meaning of fail,
But hammers and hammers away. (This line is missing from this newspaper, but appears here.—ed.)

Whenever you think you’ve come to the end
And you’re beaten as bad as can be,
Remember that diamonds are chunks of coal
That stuck to their jobs, you see.
—Minnie Richards Smith.
 
26 February 1923, The Evening Independent (Massillon, OH), pg. 11, col. 7 ad:
“A diamond is a chunk of coal that stuck to its job.”
A rich man is one who started to save and kept at it.
Keep your account at the Union National Bank growing.
 
15 September 1952, Seattle (WA) Times, “Hits and Misses,” pg. 6, col. 4:
He was a pessimist that said a diamond is only a chunk of coal, and an optimist who added, “But it made good under pressure.”—Everett Herald.
         
17 August 1962, Charleston (WV) Daily Mail, “Watch Your English” by Carroll H. Jones, pg. 21, cols. 4-5:
Diamonds: lumps of carbon that made good under pressure.
 
29 November 1962, Winona (MN)

, pg 14, col. 3:
A diamond is a chunk of coal that made good under pressure.
 
Google News Archive
13 June 1983, Kingman (AZ) Daily Miner, “Senior Scene” by Pearl Hier, pg. 5, col. 4:
A diamond is a chunk of coal that made good under pressure…
 
Google Books
Income Without a Job
By Michael Jay Anthony with Barbara J. Taylor
Lulu.com
2008
Pg. 243:
A diamond is a chunk of coal that is made good under pressure.
Henry Kissinger
 
Twitter
Body&Life Motivation
‏@TatsFashFitspo
A diamond is a chunk of coal that made good under pressure. -Unknown Author #motivation #Success
6:55 PM - 18 Mar 2015