I retract my theory on Peridot and Amethyst's fusion being Ametrine and instead believe that it is, Flourite.

Here's why-
•Fluorite promotes spiritual and psychic wholeness and development, protection, and brings peace.  Both Peridot and Amethyst stones promote peace. Development is what they both need but in different areas.

•It can be used to manifest one's life purpose. Peridot beloved life is all work and no fun, Amethyst beloved life is all fun and no work, together, they find that the true meaning is finding your own purpose and that it's a blend of work and fun that gives you balance.

•Fluorite is also used to remove astral attachments, which brings a reduction or elimination of negativite energy. Peridot is astrally attached to homeworld, a new world of possibilities with fusion.

•Fluorite is also said to enhance the strength of other stones. Amethyst and Peridot both deal with emotions and friendship, them being together would cause joy and peace between the gems.

•Fluorite is a stone of mental order and clarity. It is used to enhance mental clarity and reduce instability and disorder. Peridot can be unstable and Amethyst is disorderly, together they'd help each other combat those traits.

•Flourite brings a wiser, more balanced view of life and improves decision making. It would be balanced due to their different takes on life coming together.

• Learning is another key mental use for fluorite. It can improve learning for anyone, enhance focus and concentration, and reduce learning disorders. Amethyst has attention problems, we can all agree, and Peridot literally said, "I want to learn," to Amethyst.

•Fluorite is a great stone to calm and relieve anxiety, tension, and stress by detoxifying the emotional body. It can help get rid of mental block. Anxiety is Peridot while stress calming would be Amethyst.

•Fluorite can reduce fear of the future as well as ease anger and depression.  They would calm the others fear of the future because they see that homeworld gems can change.

•Fluorite is related primarily to the Heart and Higher Heart chakras. Both Amethyst and Peridot are used for the heart chakras.

•Multicolor (purple and green)  fluorite brings a combination of energies to enhance flexibility, free thinking, and emotional brightness. It can bring enhanced protection in the areas enhanced by all combined types and is used to repair muddy or torn areas of the aura. If the multicolor fluorite is particularly strong in one color, it will also be strong in that color's area of influence.  This means that their fusion could possibly be like Garnet and change slightly in color to show who's in control.