Stilpnomelane H2(Mg,Fe)Al2SiO7

Optical Properties:

Biaxial , but with 2V close to 0 degrees; extinction almost parallel; brown to yellow green pleochroism is distinctive.

The photographs above show golden stilpnomelane in plane polarized light (left) and under crossed polarizers (right). The photo below (uncrossed polarizers) shows stilpnomelane in a characteristic sheaf-like arrangement.

Occurrence:

Stilpnomelane occurs in some low grade, burial metamorphic rocks, with quartz, white mica, garnet, etc.

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