Tom Swift Among the Diamond Makers, Or, The Secret of Phantom Mountain, is Volume 7 in the original Tom Swift novel series published by Grosset & Dunlap.

Tom Swift flies his airship to the mountain tops of Colorado to seek for the secret of the Diamond Makers: criminal scientists who have figured out the formula of manufacturing a limitless fortune in diamonds.

Tom & friends are soon captured and left to die in a collapsing mountain.

In this story, the major invention, and plot device, is a diamond-making machine, utilizing the power of harnessed lightning.

Unfortunately for Tom and friends, they were never able to get close enough to the machinery to determine the secret to making diamonds.