pyrite

plural pyrites

1. chemistryThe common mineral iron disulfide (FeS₂), of a pale brass-yellow color and brilliant metallic luster, crystallizing in the isometric system.

   The pyrite output in 1961 was 1.2 million tons, derived mainly from the Hsiang Shan mine in Anhwei and the Ying-te mine in Kwangtung.

   1973, Chiao-min Hsieh, “Mining and Manufacturing”, in Christopher L. Salter, editor, Atlas of China, McGraw-Hill, Inc., →ISBN, →LCCN, →OCLC, →OL, page 100, column 1

   1 more example

   China's 13 large foreign fertilizer plants ordered a few years ago are all scheduled to be in operation in a year or two.[…]China's biggest pyrite mine (openpit), being built in Yunfu, Kwangtung Province, was near completion.

   1978 November 9, K. P. Wang, “China's Mineral Economy”, in Chinese Economy Post-Mao: A Compendium of Papers, Washington, D.C.: Government Printing Office, →OCLC, page 387

2. usuallyAny metallic-looking sulphide, such as the above, which is the most common.
3. solid state chemistry(usually as a plural: pyrites) Any metal dichalcogenide that is isostructural to the common mineral.

   Copper diselenide can occur both as a marcasite and a pyrite.