File:Serpentinite, Deer Lake Peridotite 5.jpg

English: The Deer Lake Peridotite (aka Deer Lake Complex) is a metamorphosed peridotite sill complex in the Precambrian-aged Ishpeming Greenstone Belt of Michigan's Upper Peninsula (UP), USA. The metamorphism has converted the original peridotite (probably dunite or close to it) into serpentinite. Good exposures can be seen next to Co. Rd. 573, along the western side of Deer Lake, northwest of the town of Ishpeming (see map). Freshly broken surfaces of serpentinized Deer Lake Peridotite from here can be wonderfully bluish-green. A slight but noticeable tug can be felt when a magnet is placed next to these rocks. Many serpentinites have a minor component of magnetite (a chemical consequence of peridotite metamorphism). The rocks shown can be slightly magnetic, despite the absence of visible magnetite crystals.

The serpentinites along the western side of Deer Lake often have thin veins of chrysotile asbestos, one of the varieties of the mineral serpentine. Older references indicate that pillow basalts are present at the Deer Lake West locality. More recently published references interpret the pillow basalt-like structures in the serpentinite as shear polyhedra or contraction joints in a shallowly-emplaced sill. Examination of the "pillow" structures in summer 2010 revealed that they are simply the result of sinuosity of asbestos (chrysotile) veins.

Age: late Neoarchean?, ~2.5-2.7 billion years.