Comic Title: Action Comics #310
Publisher: DC (National Periodical Publications, Inc.)
Address: 575 Lexington Avenue, New York, NY
Cover Date: March 1964
On Sale Date: January 30, 1964 Newsstand Date January 30, 1964
Source: House Ad, Adventures of Jerry Lewis #81, Page 30

Newsstand Date January 30, 1964
Source: Newsdealer Magazine, V19 #1

Copyright Date January 30, 1964
Source: Library of Congress, Periodicals 1964

Frequency: Monthly
Cover Price: $0.12
Page Count: 32
Editor: Mort Weisinger

Title: "Secret of Kryptonite Six"
Pages: 13

Feature(s):
Superman (of Earth-1)

Writer: Leo Dorfman
Penciller: Curt Swan
Inker: George Klein

Reprinted In:
Superman #227 (1970)
Best of DC #36 (1983)

Feature Character(s)

• Superman (last appearance in Superman's Pal, Jimmy Olsen #75; next appearance in World's Finest Comics #140)

Supporting Character(s)

• Jimmy Olsen (last appearance in Superman's Pal, Jimmy Olsen #75; next appearance in Superman's Girl Friend, Lois Lane #48)
• Perry White (last appearance in Superman's Pal, Jimmy Olsen #75; next appearance in Action Comics #311)
• Lori Lemaris (last appearance in Action Comics #309; next appearance in Action Comics #312)

Villain(s)

• Jax-Ur (last appearance in Action Comics #309; next appearance in World's Finest Comics #146)
• Professor Vakox (last appearance in Action Comics #309; next appearance in World's Finest Comics #146)
• Two unnamed Phantom Zone prisoners (no further appearances)
• A Thought-Beast (no further appearances)

Guest Appearance(s)

• Supergirl (last appearance in Superman's Pal, Jimmy Olsen #75; next appearance in Action Comics #310)

Other Character(s)

• Various Atlanteans and Kandorians (no further appearances)
• Vorb-Un (a paroled Phantom Zone prisoner; no further appearances)
• An unnamed boy and his father (no further appearances)

Comments:
This story introduces Jewel Kryptonite, which allows Phantom Zone prisoners to focus their thoughts and cause explosions in the real world.

Synopsis:
Superman releases Jax-Ur from the Phantom Zone on a trial basis when Jax-Ur claims to have a cure for an Atlantean plague. Superman and Jax-Ur use a time-bubble to travel to Krypton prior to its explosion. Jax-Ur retrieves the formula for the cure from an old laboratory in the Jeweled Mountains. He also sets up a device to send a fragment of the Mountain to Earth when Krypton explodes.

When Superman and Jax-Ur return, Superman gives the plague cure to Lori Lemaris and the Atlanteans. Jax-Ur then hypnotizes Jimmy Olsen into uses the Jewel Kryptonite fragments on Superman.

Afterwards, Superman's presence cause fuel to explode when he is near. Superman believes he must leave the Earth, until he deduces that the real cause of the explosions is the fragment of Jewel Kryptonite in Earth's orbit. The Phantom Zone criminals are able to use the Kryptonite to focus their thoughts and cause the explosions. Superman hurls the fragment into the sun, ending the threat and Jax-Ur's scheme.