The twelve gates were twelve pearls, each gate made of a single pearl.
Revelation 21:21
Words & Music: Adoniram. J. Buchanan, 1889 (🔊 pdf nwc). Appeared in Song-Land Messenger Complete, edited by Horace N. Lincoln (Dallas, Texas: H. N. Lincoln, 1892), number 109.
If you know where to get a good photo of Buchanan (head & shoulders, at least 200×300 pixels),

Have you heard of that bright city,
With its open pearly gate?
Where the ransomed ones are singing,
And the loved ones for us wait.
Refrain
Over there the angels wait,
Over there,
At the beautiful pearly gate.
Have you heard of that bright river,
Clear as crystal, pure and free?
Flowing from the throne of glory,
Soon its beauties we shall see.
Refrain
Will you go to that bright city,
With immortals will you live?
Trust in Jesus, love and serve Him,
And eternal life He’ll give.
Refrain