What is the chemical makeup, likely origin, for my ~5 pound radioactive mica?

Question

What is the likely chemical makeup and likely origin, for my ~5 pound mica that is planar on an inch scale (not large sheets) and quite radioactive?

Answer 1

Not quite sure I get your question. Most mica isn't radioactive. Perhaps you are confusing it with a radioactive mineral with a micaceous appearance such as torbernite? Please elaborate on your question.

Comments

The rock has been called a biotite mica by a geologist in AZ.  it is not green so does not look like a torbernite.  The rock emits 2 mr/hr on contact and is decidedly mica and flaky.  The question is where could such a rock come from and how might the U or Th be incorporated into the mica?

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Biotite mica is not radioactive. Perhaps it is included with a radioactive mineral such as zircon or uraninite.