DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Astrophyllite mineral. Astrophyllite is a very rare mineral, a hydrated potassium iron titanium silicate. It is triclinic and occurs as lamellar crystal aggregates in honey-brown to yellow colours. Its interest is limited to scientists and collectors only. It occurs in felsic igneous rocks in fissures and cavities. This sample, from Cheyenne Canyon in Colorado, USA, 24 centimetres across.
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