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Troctolite 76535 from the Apollo 17 landing site

Troctolite 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.

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,[1] the Stillwater igneous complex of Montana and the Tertiary Rhum layered intrusion of the island of Rùm, Scotland.[2] Troctolite is also found in the Merensky Reef of the Bushveld Igneous Complex, South Africa and in the Lizard complex in Cornwall.[3]


  1. ^ Geology of the Voisey's Bay Deposits abstract
  2. ^ Troctolite (allivalite): Isle of Rhum, northwestern Scotland
  3. ^ The Lizard
  • Blatt, Harvey and Robert J. Tracy, 1996, Petrology: Igneous, Sedimentary and Metamorphic, 2nd ed., p. 72, Freeman, ISBN 0-7167-2438-3