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- A texture sometimes observed in a thin section of a rock, in which a ring of one mineral occurs with another mineral or minerals inside and outside the ring.
- In mineral deposits, the surrounding of one mineral by a ring of one or more other minerals; commonly results from replacement of pyrite by another mineral, with the outermost pyrite unaffected and constituting the "atoll." Syn: core texture
Source: Dictionary of Mining, Mineral, and Related Terms