Mafic rock
Troctolite 76535 from the Apollo 17 landing site
olivine, calcic plagioclase, minor pyroxene

Troctolite /ˈtrɒktəlt/ (from Greek τρώκτης 'trout' and λίθος 'stone') is a mafic intrusive rock type. It consists essentially of major but variable amounts of olivine and calcic plagioclase along with minor pyroxene. It is an olivine-rich anorthosite, or a pyroxene-depleted relative of gabbro. However, unlike gabbro, no troctolite corresponds in composition to a partial melt of peridotite. Thus, troctolite is necessarily a cumulate of crystals that have fractionated from melt.[1]

Troctolite is found in some layered intrusions such as in the Archean Windimurra intrusion of Western Australia, the Voisey's Bay nickel-copper-cobalt magmatic sulfide deposit of northern Labrador,[2] the Stillwater igneous complex of Montana, the Duluth Complex of the North American Midcontinent Rift,[3] and the Tertiary Rhum layered intrusion of the island of Rùm, Scotland.[4] Troctolite is also found, for example, in the Merensky Reef of the Bushveld Igneous Complex, South Africa and in the Lizard complex in Cornwall.[5]


  1. ^ Emeleus, C. H.; Troll, V. R. (2014-08-01). "The Rum Igneous Centre, Scotland". Mineralogical Magazine. 78 (4): 805–839. doi:10.1180/minmag.2014.078.4.04. ISSN 0026-461X.
  2. ^ Sulphide segregation in the Mushuau Intrusion of northern Labrador as recorded by nickel-in-olivine magmatic stratigraphy abstract, BRADLEY, L.A. and SYLVESTER, P.J., Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NF, A1B 3X5
  3. ^ Paces, James B.; Miller, James D. (1993). "Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift System". Journal of Geophysical Research: Solid Earth. 98 (B8): 13997–14013. doi:10.1029/93JB01159. ISSN 0148-0227.
  4. ^ Troctolite (allivalite): Isle of Rhum, northwestern Scotland
  5. ^ The Lizard