Miles E. Tyrrell has written:

'Ceramic investigation in the Eufaula Bauxite District, Alabama' -- subject(s): Bauxite, Clay

'Synthetic cordierite' -- subject(s): Cordierite

Some shales, possibly some mudstones that have undergone thermal metamorphism.

it's graphite!!

Sea sediment is mud found at the bottom of an ocean. "Iolite" is another name for the mineral cordierite, a magnesium iron aluminum silicate, which is noted for unusually strong pleochroism. Transparent cordierite makes beautiful gemstones, in shades of blue.

Dolores J. Gable has written:

'Geology and regional metamorphism of some high-grade cordierite gneisses, Front Range, Colorado' -- subject(s): Cordierite, Gneiss, Petrology

'Geologic map of the Nederland quadrangle, Boulder and Gilpin counties, Colorado' -- subject(s): Geology, Maps