Hornblende gabbro is an intrusive rock similar to normal gabbro (gabbro sensu stricto[1]). In the QAPF classification it falls within the gabbro field, in which quartz makes up 0% to 5% of the QAPF mineral fraction, plagioclase makes up 90% or more of the total feldspar content, and the plagioclase is calcium-rich (%An > 50).[2][3] Hornblende gabbro is distinguished from other subtypes of gabbro by having a composition almost entirely of plagioclase and hornblende, with olivine and pyroxene each making up less than 5% of its mineral content.[1]

References

  1. 1 2 "Rock Classification Scheme - Vol 1 - Igneous" (PDF). British Geological Survey: Rock Classification Scheme. 1: 1–52. 1999.
  2. ↑ Le Bas, M. J.; Streckeisen, A. L. (1991). "The IUGS systematics of igneous rocks". Journal of the Geological Society. 148 (5): 825–833. Bibcode:1991JGSoc.148..825L. CiteSeerX 10.1.1.692.4446. doi:10.1144/gsjgs.148.5.0825. S2CID 28548230.
  3. ↑ Philpotts, Anthony R.; Ague, Jay J. (2009). Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. pp. 139–143. ISBN 978-0-521-88006-0.


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