Troctolite

Troctolite, (from Greek "troctos" and "lithos" = trout rock due to the look "spotted", due to the presence of olivine crystals, consists essentially of major but variable amounts of olivine and calcic plagioclase along with variable minor pyroxene. It is an olivine-rich, pyroxene-depleted relative of gabbro. However, unlike gabbro, no troctolite corresponds in composition to a partial melt of peridotite. Thus, troctolite is ecessarily a cumulate of crystals that have fractionated from melt. The olivine may be wholly altered to serpentine, which gives the rock a stippled appearance of red, green, brown, yellow, and black spots on a pale background, reminiscent of the skin of a trout. Serpentine alteration is common in plutonic or metamorphic rocks, it being along fracture, as the result of hydrothermal or deuteric processes and may completely convert olivine rocks in a serpentine rock, with a structure characteristic of the olivine fracture pattern ("mesh structure").



gabbrocirocks.jpg

Diagram for Gabbroic rocks. From IUSG.


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Altered olivine (yellow-orange) in a troctolite from Lofoten Archipelago, Norway. From (Sandatlas). Lødingen, Hinnøya, Norvegia.



troctolite2017(2).jpg

Altered olivine (yellow-orange) in a troctolite from Lofoten Archipelago, Norway. From (Sandatlas). Lødingen, Hinnøya, Norvegia.




Bibliography



• Eric A.K.Middlemost (1985): Magmas and Magmatic Rocks. Longman, London
• Ron H. Vernon (2004): A pratical guide to rock microstructure. Cambridge editore
• K.G.Cox, J.D.Bell & R.J Pankhurst (1979): The interpretetion of igneous rocks. George Allen&Unwin editori.
• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori


XPL image, 2x (Field of view = 7mm)
Photo
troctolite1484(2).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
troctolite1484(3).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite1484(4).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
troctolite1484(5).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite1484(6).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
troctolite1484(7).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite1484(8).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite1484(9).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
troctolite1484(17).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 10x (Field of view = 2mm)
trooctoolite(5).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
trooctoolite(6).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
trooctoolite(2).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
trooctoolite(7).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
trooctoolite(9).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
trooctoolite(3).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
trooctoolite(4).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
trooctoolite(8).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). PPL image , 2x (Field of view = 7mm)
troctolite(22).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite(23).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite(10).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)
troctolite(11).jpg

Olivine partially altered in serpentine (note the radial fracture due to increases of volume for Serpentinization). XPL image , 2x (Field of view = 7mm)