pseudomorphic

/ˌsuːdəˈmɔːrfɪk/
adjective
  1. Having a false or altered form; describing a mineral or crystal that has the outward shape of another mineral but a different internal structure.
    • Geologists found a pseudomorphic fossil where the original shell had been replaced by pyrite.
    • The pseudomorphic quartz crystal looked like a cube but was actually hexagonal inside.
    • The museum displayed a pseudomorphic specimen of calcite that had taken the shape of aragonite.
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