A green, brown, or black splintery, cleavable pyroxene mineral, essentially (Fe,Mg)2Si2O6.
[French hypersthène : hyper-, extreme (from Greek huper-; see HYPER-) + Greek sthenos, strength; see segh- in the Appendix of Indo-European roots.]
hy′per·sthenic (-thĕnĭk) adj.
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