You can use the Industrial Foregoing Ore Dictionary Converter to convert items with sharing oredict entries into each other, whereby you can input all items that share the specified entry, however you may only output those items, that have the specified entry as their first entry.
Many gems share the gemAll oredict as entry, most of them as their first. That means, one can turn each of those gems into most of the other gems.
The following gems can be turned, at an instant 1 to 1 ratio:
Diamond, lapis, emerald, quartz, amethyst, garnet, opal
into the following gems:
Diamond, emerald, quartz, amethyst, garnet
Yes. Unlimited diamonds.

You can use the Industrial Foregoing Ore Dictionary Converter to convert items with sharing oredict entries into each other, whereby you can input all items that share the specified entry, however you may only output those items, that have the specified entry as their first entry.
Many gems share the gemAll oredict as entry, most of them as their first. That means, one can turn each of those gems into most of the other gems.
The following gems can be turned, at an instant 1 to 1 ratio:
Diamond, lapis, emerald, quartz, amethyst, garnet, opal
into the following gems:
Diamond, emerald, quartz, amethyst, garnet
Yes. Unlimited diamonds.