ANSWER REVEALED BELOW
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MATERIAL: I am a sodium aluminum silicate mineral.
DESCRIPTION: I am deep blue in color from the sulfur trapped inside the crystal structure and have white streaks running through me. I do not contain metallic inclusions (like pyrite) nor lazurite.
FORMATION: I form in metamorphic rocks such as marble.
METAPHYSICAL USES: I am believed to support communication, truth, and mental clarity.
It was really hard to find an image that didn't give it away. These might, but here goes...