4 words for CQZ 1–3 letters

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1 letter (3)

c q z
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3 letters (1)

zcq
Form of quartz with coloured bands
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A
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G
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Hint 1 meaning
A semipellucid, uncrystallized variety of quartz, presenting various tints in the same specimen. Its colors are delicately arranged in stripes or bands, or blended in clouds.
Hint 2 anagram
AEATG
Hint 3 another clue
CERTAIN BRAIN SIZE
7 +1