thuringite

from The Century Dictionary.

• noun In mineralogy, a hydrous silicate of iron and aluminium, occurring as an aggregate of minute scales which are distinctly cleavable in one direction, and have an olivegreen color and nacreous luster.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Min.) A mineral occurring as an aggregation of minute scales having an olive-green color and pearly luster. It is a hydrous silicate of aluminia and iron.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy A hydrous silicate of iron and aluminium occurring as an aggregation of minute olive-green scales