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Named for the Greek dyo, from which the prefix di- gets its origin to represent “two,” and opsi, meaning “face,” in reference to the two possible orientations of the vertical prism. Diopside is a relatively common mineral that can be found of fine quality in localities in Austria, Italy, Finland, Russia, Canada, the United States, Madagascar, China, Afghanistan, India, and Pakistan, among many other general localities. It occurs commonly in skarn, calcium and magnesium rich gneiss and schist, kimberlites, and peridotites and is typical of metamorphosed silicious calcium and magnesium rich rocks in the pyroxene-hornfels and epidote-amphibolite facies. Less commonly, Diopside can be found in alkaline olivine basalt and andesite.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/diopside.pdf